Multiplying and Dividing in 10s

Multiplying and Dividing in 10s

Basic

Multiplying by 10, 100, 1000, moves the digits in each column (units, 10s, 100s, etc) to the left:

• multiplying by 10 moves all the digits 1 column to the left;

• multiplying by 100 moves the digits 2 columns to the left;

• multiplying by 1000 moves the digits 3 columns to the left.

multiplying by 10s

Dividing by 10, 100, 1000 moves the digits in each column to the right:

• dividing by 10 moves them 1 digit to the right;

• dividing by 100 is 2 digits right;

• dividing by 1000 is 3 digits right.

dividing by 10s

The same is true for decimal numbers. Although the digits move, the decimal point stays in the same place.

multiplying decimals by 10s

dividing decimals by 10s

Examples

1. What is 34 x 100?

Answer: 3400

Move the 34 two digits to the left, filling the empty spaces with zeroes.

2. Given 34 x 23 = 782, what is 34 x 230?

Answer: 7820

230 = 23 x 10, re-write the question as 34 x 23 x 10.  That makes the answer 10 times larger than the original question.