Bài 8: Multiplying two digit by two digit number

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https://www.youtube.com/watch?v=vak31YAMkHI&list=PLpCAXStFkK0HJfkEi1ZxxLkc2OhvNeh1m&index=6

          

Jojo is thinking. Jojo, what are you thinking?

You know, I am going to be the richest in the jungle.  

When? How? I heard a merchant say that one mango can be sold for 5 coins.

I have 12 mango trees in my orchard and there are 25 mangoes on each tree.

So, how many coins will you get then? I don’t know. Let’s find out.

To find out the number of coins, we must first find out the number   of mangoes.

There are 12 trees and each tree has 25 mangoes.

So, the total number of mangoes would be the product of 12 and 25.

Number of trees = 12

Number of mangoes on each tree = 25

Total number of mangoes = 12 x 25

Do you know how to multiply? Yes! I do. But I can only multiply a number with one digit.

But here, we need to multiply with a 2 digit number.
Ok, I will teach you.

As you know we start in the one places.

Step 1: Multiply by ones. First multiply 5 by 2 we get 10. Put down 0 and carry  1.

Now, multiply the tens of the top number with the one on the bottom number.

That is 5 multiply by 1 is equal to 5, add 1 to 5 we get 6.

We have finish multiplied the top number with the one of the bottom number.

The product of multiply the first digit was placed on the first line.

The product of multiply the second digit will go on the second line.

Step 2: Multiply by tens. 
The second number multiply is 2 which is in the tens place or 20, take 0 from the 20 and places on the second line.

Now, multiply by 2. 2 multiply by 2 is 4. Put down the 4.

Next, multiply 2 by 1 we get 2.
This is very important to keep your number in the strip line.

Step 3: Add. 
Add the two products. 
That is 60 plus 240 we get 300.
0 plus 0 is 0, 6 plus 4 is 10, put down the 0, caring the 1.

Now, add 1 plus 2, and we get 3. 
So 12 multiply by 25 is equals to 300.

You have a total of 300 mangoes. And one mango can be sold for 5 coins.

So, Jojo will get 300 multiply by 5 coins. 
Jojo, can you multiply 300 by 5?

Yes, it’s 1500 coins. Wow! You would be so rich. But what will you do with all that money?

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