Bài 15: Multiplication by carrying over

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Yes Starry, you guessed right!
This is another lesson and multiplication.

But you will learn something new and I’m sure you will find it interesting.

Before I go any further let me see if you remember what the multiplicative and the multiplier are.

Oh! Do you remember Starry?

The number to be multiplied is called the multiplicand and the number by which we multiply is called the multiplier.

Today, I will teach you multiplication by carrying over.

Now, what do we mean by caring over?

Let me explain,

Suppose we have to multiply a two digits number 23 by 4.

We begin by arranging the multiplication vertically.

Next, we multiply the units digit 3 in 23 by 4.

The product is 12.

The number 12 has 2 in the units place and 1 in the tens place.

Write the 2 of 12 in the units place of the product.

Starry, I know you are wondering what to do with the one tens of the number 12, you carry over the 1 tens from 12 to the tens column and write the 1 tens above the tens in the multiplicand.

That is about 2.

Now multiply the tens digit 2 in 23 by 4, we get 8 tens.

Add to this the carried over 1, we get 9 tens, write it in the product in the tens place. The product is 92.

Wasn’t that easy?       

Starry, help me multiply 19 by 4.

We first multiply the units digit 9 in 19 by 4. The product is 36.

Write the 6 of 36 in the units place of the product, carry over the 3 tens from 36 to the tens column and write the 3 above 1.

Now multiply ten digit 1 in 19 by 4, we get 4 tens.   

Add to  this the carried over 3, we get 7 tens.

Write it in the tens place in the product.
The product is 76.

Now Starry, here the multiplication that is slightly different.

Suppose we have to multiply 43 by 5.

Multiply the unit digit 3 in 43 by 5. The product is 15.

Write the 5 of 15 in the units place of the product.

Carry over the 1 ten from 15 to the tens column and write the 1 above 4.

Now multiply the 4 tens in the multiplicand by 5. The product is 20 tens.

Add to this the carried over ten, 20 tens plus 1 ten equals 21 tens.

Write 1 in the ten places in the product and make a new place to write the 2 hundreds. The product is 215.

Come Starry, let me see if you have understood, let us do the next one together.

Multiply 85 by 9.

Multiply the units digit 5 in 85 by 9. The product is 45.

Write the 5 of 45 in the units place of the product.

Carry over the 4 tens from 45 to the tens column and write the 4 above 8.

Now multiply the 8 tens in the multiplicand by 9, the product is 72 tens.

Add to this the carried over 4 tens, 72 tens plus 4 tens equals 76 tens.

Write 6 in the tens place and 7 in the hundreds place in the product. The product is 765.

And now we will revise what we have learnt.

Multiply 29 by 2.

We first multiply the units digit 9 in 29 by 2, the product is 18.

Write the 8 of 18 in the units place of the product,

carry over 1 tens from 18 to the tens column and write it above 2.

Now multiply the tens digit 2 in 29 by 2, we get 4 tens.

Add to this the  carried over 1 tens, we get 5 tens, write it in the tens place in the product.
The product is 58.

Multiply 18 by 5.

First, multiply the units digit 8 in 18 by 5, the product is 40.

Write the 0 of 40 in the units place of the product.

Carry over the 4 tens from 40 to the tens column and write it above 1.

Now multiply the tens digit 1 in 18 by 5, we get 5 tens.

Add to this the carried over 4 tens, we get 9 tens, write it in the tens place in the product. The product is 90.

Finally, let multiply 70 by 4.

Multiply the units digit 0 in 70 by 4, the product is 0.

Write the 0 in the units place of the product.

Next, multiply the 7 tens in the multiplicand by 4, the product is 28 tens.

Write 8 in the tens place, and 2 in the hundreds place in the product. The product is 280.

Starry, you have now learnt how to carry over to the tens place while multiply two digit numbers

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