Bài 17: Multiplying a three digit by a one digit number

Carrying over, Starry do you remember, what carrying over is?

We learn about it when multiply two digit numbers.

Oh, you have forgotten? Don’t worry, we will revise it.

Let see we multiply 12 by 7.

We begin by arranging the multiplication vertically.

Next to be multiply the unit digit 2 in 12 by 7.

The product is 14, we write the 4 of 14 in the unit places of the product.

And carry over the 1 ten from 14 to the ten column and write it above the ten in the multiplicand that is above 1.

Now multiply the ten digit 1 in 12 by 7, we get 7 tens, add this carry over 1, we get 8 tens.

Write it in the product in the ten places.

The product is 84. Starry, that was multiply two digit number by a one digit number by carrying over to the ten places.

Now let us see how to multiply a three digit number by a one digit number again by carrying over to the ten places.

Multiply 224 by 3.

First arrange multiplication vertically, next we multiply the unit digit 4 in 224 by 3. The product is 12.

The number 12 has 2 in the unit places and 1 in the ten places.

Write the 2 of 12 in the unit places and carry over the 1 ten from 12 to the ten column.

And write it above the ten in the multiplicand that is above 2.

Next multiply the ten digit 2 in 224 by 3, we get 6 ten.

Add this with carry over 1, we get 7 tens.

Write it in the product in the ten places.

Multiply the hundred digit 2 in 224 by 3, we get 6 hundreds.

Write it in product in the hundred places. The product is 672.

Oh, wasn’t that long Starry? Yes, but very easy.

Now will you help me do another one Starry?

Let us multiply 318 by 2.

First multiply the unit digit 8 in 318 by 2, the product is 16.

Write the 6 of 16 in the unit places and carry over the 1 ten in 16 to the ten column,

write the 1 ten above the ten in the multiplicand, that is above 1.

Next, multiply the ten digit 1 in 318 by 2, we get 2 tens.

Add this with carry over 1, we get 3 tens.

Write it in the product in the ten places.

Multiply the hundred digit 3 in 318 by 2, we get 6 hundreds.

Write it in the product in the hundred places. The product is 636.

Now let us revise what we have done.

Multiply 119 by 3.

First multiply the unit digit 9 in 119 by 3, the product is 27,

write the 7 of 27 in the unit places and carry over 2 ten from 27 to the ten column.

Write the 2 ten above the ten in the multiplicand, that is above 1.

Next, multiply the ten digit 1 in 119 by 3, we get 3 tens.

Add this with carry over 2, we get 5 tens.

Write it in the product in the ten places.

Multiply the hundred digit 1 in 119 by 3, we get 3 hundreds.

Write it in the product in the hundred places. The product is 357.

Now one last multiplication, multiply 109 by 9.

First multiply the unit digit 9 in 109 by 9. The product is 81.

Write the 1 of 81 in the unit places, and carry over the 8 ten from 81 to the ten column.

Write the 8 ten above the ten in the multiplicand that is above 0.

Next, multiply the ten digit 0 in 109 by 9, we get 0 ten.

Add this carry over 8, we get 8 tens.

Write it in the product in the ten places.

Multiply the hundred digit 1 in 109 by 9 , we get 9 hundreds.

Write it in the product in the hundred places. The product is 981.

Starry, Wasn’t that a good lesson on multiply a three digit number by a one digit number.

I sure you enjoy this.