BÀI 19 : FIND PERCENTAGES OF NUMBERS- TÌM TỶ LỆ % CỦA SỐ

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https://www.youtube.com/watch?v=uRimkk9tsXI

What is 10% of a million dollars.

exactamente 10% is $100,000 .

go gogo … 

To find 10% of a million dollars, we simply move the decimal point one place to the left.

If  we had 10 stacks of cash on a table and each stack was $100,000 ,we would have a million dollars.

 one stack equals one tenth  which is $100,000.

10 / 10 would be all 10 stacks equals $1,000,000.

wrote…… chut cha chut cha-ching oh yeah.

Let’s try another problem.

 What  is 60% of 80 dollars.

Well, what's 50% of 80 dollars.

 That 's right $40.

Now  what's 10% of 80.

 Remember, To find 10% , we can just move the decimals one place to the left.

So 80 becomes 8.
40 plus 8 equals 48 and that's our answer.

How  about 65% of 80.

We  know that 50% of 80 is 40.
 and we know that 10% of 80 is 8.

5% is half of 10% .

So  half of 8 is 4 .

And  if we add it all up ,we have 52 .

65% of 80 is  52 .

Let 's try a tricky one .

What  is 15% of 70 .

To  solve this,we need to find 10% and 5% to give us  15%.

So  what's 10% of 70.

That 's right.

We  move the decimal one to the left to give us seven .

And   five percent is half of 10%.

So  what's half of seven .

That 's right.

Three  point five .

Seven  plus three point five is ten point five .

So  ten point five is our answer.

 ro room yes hi yeah .

Let 's do one more.

What  is one percent of five million dollars .

ruah thousand dollars.

 So  100 percent of five million dollars is five million dollars.

 To  find 10 percent we just move the decimal one space to the left .

To  find one percent ,we would move the decimal two spaces to the left.

 So $50,000 is one percent of five million dollars .

Roku Mulla Mulla Mulla hey yeah hey yeah .

Good job.

 Hopefully  these tricks make it easier keep practicing and you'll get

better and fast.

 bang bang Koston

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BÀI 18 : DIVIDING DECIMALS.

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https://www.youtube.com/watch?v=brzZNmByyM4

Alright guys .

Now  let's look at dividing decimals .

Ooh  sounds scary but it's really not okay.

 So  we have two point four five divided by one point five .

And the first thing you want to do is take that second number or the divisor and make it an integer .

So  to do that we want to move the decimal.

 One  place to the right or multiply by ten it's another way of thinking about it.

But  ultimately we just want to make one point five into 15 .

Now  you'll notice we moved it one decimal place to get it into an integer .

And  we want to do the exact same thing with the first number.

So  we had two point four five .

We 're gonna make that twenty four point five because we move the decimal place one time in the first number .

We 're gonna do that now with this number .

Okay  so now the problem reads.

 Twenty  four point five divided by fifteen .

Okay so let's look at that and make that long division .

Okay  so we have twenty four point five.

 Now  this is the real tricky part you want to make sure that the first Number that we had before.

 Twenty four point five goes inside the house .

So it kind of looks like it's doing this criss-cross thing right .

Twenty  four point five goes in the house .

The division house as we say.

 And  fifteen goes out front .

The  other really important thing here is that you make sure to put the decimal place .

Right above where it is inside the house.

 So twenty four point five ,the decimal place is right after the four .

Make  sure the decimal point is right above that in your answer .

Now  we just divide left to right just the way that we do long division.

Okay  so we ask ourselves how many times does fifteen go into twenty four .

We  don't go over that now.

 But you'll recall there's a lot of different strategies how to figure that one out.

 15 goes into 24 one time.

 So  15 times one is 15 .

24 minus 15 is nine .

Okay  so that's our remainder there step.

 We 're gonna go ahead and bring that five straight down .

So  we're left with a remainder of 95.

 Okay  so how many times does 15 go into 95 .

We  ask ourselves again .

We 're not going to go over that particular concept now.

 But  you'll see that if you work it out ,you'll get 6.

 Ok so 15 times 6 is 90.

 95 minus 90 is 5.

 Ok so now what do we do.

 Well  we're gonna imagine that there's zeros going on for.

You  tell infinity after 24.5 .

Because remember there actually are zeros that go on to infinity after twenty four point five .

So  it's twenty four point five zero zero zero zero zero and so on.

So  we're gonna bring that zero down and we get 50 .

So  how many times is 15 go into 50.

Well  again if you work it out ,it's three so 15 times 3 is 45.

Now  watch out 50 minus 45 is five .

Now  check it out.

That 's exactly what we got on the step before .

Okay  now that's interesting .

What happens if we bring down that next zero.

Well  you'll see that you get this unending stream of 50 minus 45.

And you're gonna get three on to infinity .

So this is one of those cases where.

We  can stop.

We  can stop and say this decimal is going to keep repeating.

So  we have one point six three repeating.

As  our answer.

And  that's it .

That 's how you divide decimals.

You  just move the decimal in the divisor enough times to get an integer.

And  then move the decimal the same number of times in the dividend .

And  then do long division the way you normally do it.

And that my friends is how you divide decimals.

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BÀI 17 : MULTIPLYING DECIMALS.

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https://www.youtube.com/watch?v=zEHbLRHxQpE

The following is a selected video from yourteacher.com  where you can browse over 450 complete math lessons with example videos interactive practice problems self tests and more try a complete lesson today at yourteacher.com

To multiply decimals .

Sixteen  point one times two point four.

First  line up the numbers .

Then  multiplies though we were multiplying whole numbers .

So  we can think of this problem .

As  161 times 24.

Now multiplying 4 times 1 is 4.

 4 times 6 is 24 .

So  we bring down a 4 and carry the 2 .

4 times 1 is 4 plus 2 is 6.

Now starting a new row and beginning in the tens column .

We  have 2 times 1 which is 2.

2 times 6 which is 12 .

So  we bring down a 2 and carry the 1 .

2 times 1 is 2 plus 1 is 3.

Now  we add the rows together 4 plus 0 is 4 .

4 plus 2 is 6 .

6 plus 2 is 8 .

And we bring down the 3 so that we have 3860 for .

Our  final step is to determine where the decimal point goes in our final answer.

 Notice  that since there's one digit to the right of the decimal point

and 16 point one and one digit to the right of the decimal point in 2.4.

We have the total of two digits to the right of the decimal point in our original numbers.

 This  means we'll have two digits to the right of the decimal point in our final answer.

 So  16 point one times two point four is thirty eight point six four.

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BÀI 16 : SUBTRACTION OF DECIMALS

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https://www.youtube.com/watch?v=XTqsWWRC_4k

Oh

Subtract.

 Let 's find 1 point 6 minus 0.4.

Start  by subtracting the 10^th.

 6 tenths minus 4 tenths equals 2 tenths.

 Remember to write the decimal point.

 Now  subtract the ones won 1-0 ones equals 1 1.

 So  1. point 6 minus 0.4 equals 1 point 2.

Subtract  find 4.85 minus 3.2 5 .

Subtract the hundredths five hundredths minus five hundredths equals zero hundredths.

subtract the tenths.

 Eight  tenths minus two tenths equals six tenths.

 Write  the decimal point.

 Subtract  the ones for one's minus three ones equals 11.

 4.85 minus 3.2 5 equals 1.60 or 1.6.

Subtract  find 26.6 9-10 point four three.

Nine  hundredths minus three hundredths equals six hundredths.

 Six  tenths minus four tenths equals two tenths.

 Write  the decimal point .

Six  ones minus zero ones equals six ones .

To  tens minus 1 10 equals 1 10.

 26.6 9-10 point 4 3 equals sixteen point two six.

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BÀI 15 : ADDITION OF DECIMALS

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https://www.youtube.com/watch?v=nHwMn7kAYiE&index=14&list=PLYVhl_y4T2iRMYH3o9xmfflM_deCb1wyq

Now, this lets me take a look at addition of decimals.

Now , I've drawn a pup there a puppy dog.

BUP because in addition of decimals ,we keep the point under point

okay .

PU P point under point.

Very Important.

 Let 's look at some examples.

First  one four point five plus six point nine .

Now , it's very important that you write this out on pen and paper when you do your working, okay.

 And  you set it up such that point is under the point.

 Let 's bring some working out space to show you what I mean.

 Four  point five plus six point nine you can see that the point is under the point .

So  we simply add now it's very easy.

 Five  plus nine is fourteen we put the four down and carry the one and then what have we got point under point okay we put the point in our answer.

Next  line 1 plus 4 is 5 plus 6 is 11 .

So  11 we have.

 So  the answer simply 11.4.

Okay  it's pretty easy.

 The  next one, three point seven five plus two point four six again.

 Let 's get some working out space.

This  is what you'll do three point seven.

Five  plus two point four six the point is under the point.

5 plus 6 is 11 put  the 1 down and carry the 1.

1 plus 7 is 8 plus 4 more is 12 .

So  for 12 put the 2 down and carry the 1.

Point  under point .

One  plus three is four plus two more is six .

So  answer there six point two one.

The  next one
5.9 plus fifteen point eight seven.

All  right now this is where it's very important our point under point .

Five  point nine plus fifteen point eight seven.

 You  can see the point is under the point.

And  then if we look at our decimal part hmm seems to be a gap there.

 Any  gaps we see we're going to fill up with zeros.

Okay , very important.
Ok particularly , when We  get to subtraction it's very important then. But we'll practice in addition as well .

So we have zero plus seven well that's seven.

9 Plus 8 is 17 so we put the 7 down and carry the 1.

Point  and the point.

Now  we've got two fives that's ten five and five is ten and one more is eleven with the one down and carry the one .

And finally one plus one is two.

 So  answer there 21 point seven seven.

Our  final question.

184 plus 12 plus 0.5 .

Okay  three numbers.

We 're adding this time.
 So let's get some working out space .

One  at a time 3.8 four there.

 It  is now we're adding 12.

 hmm I don't even see a decimal point there .

But if you have a whole number even though you don't see the decimal point is at the end of the number so that will be 12 point .

The 0.5 or let's write that out carefully .

Making sure that we keep the point under the point.

Okay  so there we have point under point nicely .

And  we have some spaces .

Mm  okay ,got some places to fill up what are we going to fill them up with zeros.

Okay  once we've done all that then it's the easy part.

4 plus 0 plus 0 is 4.

Eight  and zero is 8 plus 5 is 13 .

So  we put the 3 down and carry 1.

Point  under point .

Okay  make sure you put the point in your answer.

All  right what have we got on the top.

One  plus three is four plus two more is six .

And  nothing else so we have six.

 And finally just one there .
So answer there sixteen point three four.

Excellent, well that concludes the lesson  good luck with your questions

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BÀI 14: DECIMALS: SỐ THẬP PHÂN

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https://www.youtube.com/watch?v=e1bWoNpxsKE

Welcome to decimals .

We 're used to seeing numbers like this.

 But  what about this.

This  dot here shows us that this number is not 24.

 This  is our whole number or our unit.

 We  have two units .

This  is called a decimal point .

And  this is how many tenths we have.

 Tenths  are a part of a whole number .

Numbers  after the decimal are similar to a fraction

They  represent part of a number.

 2.4 is in between 2 & 3 .

We  can see this more accurately when we add in the tenths.

In between every whole number ,there are ten tenths.

If  we put an arrow showing us where two-point-four goes.

This  is where it would be pointing it is 4/10 more than to.

Let  me show you how this looks using pizza .

This  is one pizza.

Here  we have two pizzas .

Here  is where our decimal point would go if we knew that, we had more than two pizzas and less than three pizzas.

This  is what two point four pizzas look like see.

We  have two whole pizzas and only part of the next pizza.

Let 's check that 12.4
See,We  have four slices of a pizza that was cut into ten pieces. 

Someone  must have eaten the other six slices.

So  we only have two point four pizzas left.

In  activity one, you will have to color in the amount you have using pictures.

Two  point four colored in looks like this.

Another  way to show how many of something we have is using a place value table.

We  have two units and so we write two in the unit's column .

The decimal goes in the decimal column.

And  I wonder if you can guess what goes in the tenths column.

That 's right it's a four because we have four tenths .

After  the decimal the further away from the point the smaller than number .

In  activity one, you learn about tenths and hundredths .

In this activity, you will have to fill in the place value table and color in one of the grids .

This  is how 1.92 looks in a place value table .

We  have it are one unit or whole our decimal in our decimals column.

We  have nine ten and two hundredths .

This  is a blank coloring grid and when we've colored it in 1.9 - looks like this.

Use  your imagination to think about how much pizza that is.

We  color in one unit because we have one of them .

We color in nine tenths because we have nine of them.

And  we color in two hundredths because we have two of them.

 So  we fill in the table and we color in the coloring grid.

When  you are done for each number ,you should have a table that's filled in and a colored grid.

 It  is now time to start activity one .

Make  sure you watch this video again if you're still unsure about

anything.

 If  you have any questions, make sure you either write them down for me to answer for you next time or ask your teacher for help.

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BÀI 19: ANGLES - ACUTE, OBTUSE, RIGHT, STRAIGHT

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https://www.youtube.com/watch?v=vM6zued_V5Q

Angles .

Angles  are all around us.

Angles are formed when two lines meet .

If  there are two straight lines such that they have a common endpoint.

Then  the amount of turn (curl) between these two lines is known as angle between those lines.

There are angles in most shapes and in many of the objects you see and use on a daily basis .

Angles  are measured in degrees.

There  are four types of angles: acute angle, obtuse angle ,right angle, straight angle .

Let's find out more about these different types of angles.

Acute  angle

When  two straight lines make an angle with each other such that it is greater than zero degrees and less than 90 degrees.

Then  these lines are said to be making an acute angle with each other.

Some  triangles have acute angles.

Here  are a few examples the slice of pizza that you eat for lunch is an acute angle.

You  get a new box of pencils to take to school after you sharpen all of the pencils you notice that the tips are acute angles.

Obtuse  angle.

When  two straight lines make an angle with each other such that it is greater than 90 degrees and less than 180 degrees.

Then  these lines are said to be making an obtuse angle with each other.

Many shapes such as pentagons, octagons and triangles have obtuse angles.

Let 's see what makes an obtuse angle .

You are walking by the water and you see a beautiful sailboat.
You notice that the sails have obtuse angles.

You  are playing outside with friends when you look up and notice that the top of your house is an obtuse angle.

Right  angle.

When  two straight lines are perpendicular to each other or make 90 degrees with each other. then they are said to be at right angles.

 Right  angles are often shown with a box in the corner that let you  know that it is exactly 90 degrees.

Squares  and rectangles are formed using right angles.

Let 's look at a few examples.

You  are looking out the window of your house .

You notice that the window panes are formed by right angles.

You  are exploring a new city with your family .

You  notice that many of the buildings are built out of brick.

The bricks all form right angles.

Straight  angle .

When  two line segments point exactly in the opposite direction and form a single straight line ,then the angle they form is a hundred and eighty degrees or straight angle.

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