1.6 Checking your answer

Unfortunately, it is possible to get the wrong answer when using a calculator. This is not an indication of the unreliability of modern electronic technology; it’s an indication that a calculator is only as good as the fingers that press the keys! It is easy to press the wrong key, or to press keys in the wrong order, and hence to end up with a meaningless answer. It is therefore good practice to check the numbers that appear in the display as you key them in, and to repeat a calculation if the answer seems suspicious. This begs the question of how you know if the answer looks suspicious.

There are a few simple things to look out for: when adding positive numbers, the answer should be bigger than the largest of the numbers you are adding; and when subtracting one positive number from another the answer should be smaller than the larger of the two numbers. When you multiply two positive numbers, each larger than 1, the result should be larger than either of the numbers, and dividing one positive number by another that is larger than 1 should produce a result that is less than the first number.

In addition, it is good practice to estimate the answer to a question using simpler numbers. For example, you could estimate the answer to by working out (in your head) , which is 2. You would expect the answer to to be fairly close to the estimated answer.