Especially now that we have access to technology which can calculate accurately and quickly, the skill of estimating becomes very important. This is the skill that lets us know when we are multiplying 5.72 by 10.281 that the answer will be around 60. Although this won’t give us the perfect answer (which is 61.8332) it helps us check the output of a calculator isn’t widely wrong because of a typo or some other error (for instance if the calculator showed 618.332).

Example

a) 9.7 x 3.1

b) 81.4 x 98.2

c) 19.2 x 49.1

d) 102.7 / 19.6

Exercise

Let’s complete exercise 7 on pages 261 and 262 of the core textbook:

The answers are below: