Hi Paul,

The technique of using compatible numbers to estimate an arithmetic calculation involves finding numbers close to the numbers in the original problem where the arithmetic is easy. For example suppose you need to multiply 7.3 and 19.7. Notice that 7.3 is approximately 7 and 19.7 is approximately 20 so 7.3 times 19.7 is approximately 7 times 20. But 7 times 2 is 14 so 7 times 20 is approximately 140. All of this of course you do in your head so when faced with 7.3 × 19.7 I know the answer is approximately 140.

For your problem of 23.52 divided by 11.04 I immediately approximate 11.04 by 11. What number close to 23.52 is divisible by 11? What is the quotient of this number by 11?

Penny