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Part 2:
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Basic Arithmetic Skills |
| Estimating and Checking It is amazing that people frequently accept the calculator answer to a problem as being automatically correct without having a rough idea of the sort of answer they should be expecting. When we estimate the answer to a calculation we do a VERY QUICK calculation, using simplified numbers, which should be easy enough to calculate in our head, in order to get a VERY ROUGH IDEA as to what the answer will be. That way, if we key the numbers into our calculator and end up a mile away from our estimate, we will know that something is wrong. For example, suppose you have to calculate the total cost of 187 books at £11.95 each. A rough idea of the correct answer could be to calculate the cost of 200 books at £12 each, which you could do in your head and get an answer of £2,400. You can get this answer in less time than it takes you to pull your calculator out of your pocket. The correct answer to the calculation 187 × 11.95 is £2,234.65 and your estimate is quite close to this. Then, if you key in the actual calculation and get a calculator display of 22346.5 which is about ten times larger than your estimate, you would know that you had keyed something in wrongly. In fact, you put the point in the wrong place. |
