Bài 17: Subtracing with borrowing

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Starry, what are you thinking about?

Oh, so you are solving the example of subtraction.

Starry, you seem to have forgotten how to subtract by borrowing, right?
Ok, let’s practices.

Let’s begin 53 minus 7. 
Now, 3 units minus 7 units is not possible as 3 is less than 7.

So we need to take help from the digit in the tens place.

That is we need to borrow a ten from the tens place.

So, the tens place now has 1 less, that is 4.

But the units place has tens more, so instead of 3 .
It has 13.

Now, let’s subtract 13 minus 7 equals 6, we write 6 in the units place.

Now, the 4 in the tens place has no number below it for subtracting,

So we  write the 4 in the tens place of the answer.

So the answer is 46.   

Have you follow Starry?
Good!

 Let’s try this.
 70 minus 34.

Observe the units place, 0 is smaller than 4.

So from 0, we cannot subtract 4, 
we borrow ten from the tens place.

The digit in the tens is reduce by 1, and become 6.

But the units place is increase by 10, and become 10.

Now 10 units minus 4 units equals 6.

And 6 tens minus 3 tens equals 3.
So the difference is 36. 

Now Starry, look at this example 421 minus 159.
Here 1 unit is less than 9 units.

So we borrow a ten, the digit in the tens place is reduce by 1,

and the digit in the units place is increase by 10 and become 11.

11 minus 9 equals 2. 
Observe that, the 1 tens is less than 5 tens.

So we need to borrow again.

But this time from the hundreds place, so the hundreds place is reduce by 1 to become 3.

The tens place is now increase by 10 and become 11, 11 tens minus 5 tens equals 6 tens.

Since the digit 4 in the hundreds place is reduce by 1, it become 3.

Now, 3 hundreds minus 1 hundreds equals 2 hundreds.
 So the difference is 262.

Let’s see another example .
500 minus 126.

If you observe carefully, 0 units is less than 6 units.

We cannot subtract 6 from 0. 
We need to borrow from the tens place.

But look, even the tens place has the 0.

So we cannot borrow from the tens place either.

Now, what do we do?
Starry, we now go to the hundreds place.

The hundreds place has 5, 
we borrow ten for the tens place.

Hence, the hundreds place now has 4, and the tens place now has 10,

We now borrow a ten from the tens place for the units place.

The tens place is left with the 9.

Now 10 minus 6 equals 4, 9 minus 2 equal 7, and 4 minus 1 equal 3.

So the difference is 374.
Is it borrowing easy Starry?

Oh, so you want to solve another example 
Fine, here it is 823 minus 269.

Now 2 units has smaller than 9 units.
Hence, we cannot subtract 9 from 2.

So what do we do Starry? 
Right! We borrow ten from the tens place,

from 3 tens when we subtract 1 tens we get 2 tens.

This 1 tens when we add to 2 units we get 12 units.

Now 12 is greater than 9.
So 12 minus 9 equal 3.

Observe the tens place Starry, it has 2 tens which is less than 6 tens.

So, We borrow tens from the hundreds place.
The hundreds place has 8, when we borrow tens, the hundreds place become 7, and the tens place become 10 plus 2 equals 12.

So 12 tens minus 6 tens equal 6, and 7 hundreds minus 2 hundreds equals 5 hundreds.

So the difference is 563.

Now let’s quickly go to what we have learn today.
Subtract 312 minus 113.

We cannot subtract 3 from 1.
So we borrow 1 ten from the tens place.

Now the tens place is left with 1 ten, and the units place is 10 plus 1 that is 11.

So 11 minus 3 equals 8.

Now 1 ten minus 1 ten equals 0 ten, and 3 hundreds minus 1 hundred equals 2 hundreds.

So the difference is 208.

Let’s solve this.
 802 minus 486.

Now, we cannot subtract 6 from 2, so we go to the tens place for borrowing.

But the tens place has a 0, so we go to the hundreds place to borrow,

now 8 hundreds become 7 hundreds, and 0 tens become 10 tens,

we borrow a ten for the units so we get 9 tens, and 10 plus 2 units that is 12 units,

12 minus 6 is 6, 9 minus 8 equals 1, and 7 minus 4 equals 3.

So the difference is 316.

Let’s try this one .
444 minus 8.
4 units are less than 8 units.
So we cannot subtract 8 from 4.

So we borrow from the tens place, the tens place become 3, and the units place become 10 plus 4 that is 14.
Now 14 minus 8 equals 6.

In the tens place and the hundreds place there is no number to be subtractive.

So we write down 43 as this.
So the difference is 436.

Good! You have picked up subtraction very quickly.
Keep it up.

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