Adding, multiplying, and performing similar mathematical operations in one's head can be difficult tasks, even for the most skilled mathematics students. By estimating, however, basic operations are easier to calculate mentally. This can make daily calculation tasks, from figuring tips to monthly budgets, quickly attainable and understandable.

How to Estimate

Although the core of estimation is rounding, place value (for example, rounding to the nearest hundreds) makes estimating flexible and useful. For instance, calculating 2.4 + 13.7 – 10.8 + 8 – 124.2 – 32 to equal –142.9 in one's head may be a daunting task. But if the equation is estimated by 10s, that is, if each number is rounded to the nearest 10, the problem becomes 0 + 10 – 10 + 10 – 120 – 30, and it is easier to calculate its value at –140. Estimating to the 1s makes the equation 2 + 14 – 11 + 8 – 124 – 32 = –143, which is more accurate but more difficult to calculate mentally. Note that the smaller the place value used, the closer the estimation is to the actual sum...