Estimating

Often we do not need an exact count: a good guess, an estimate, is enough. Your headmaster may know exactly how many students are in your school, but you might only know it is about 400, or about a thousand. Going to the shop, you estimate the cost and take a little more money than your estimate, so you never fall short.

Paromita's section has 32 children. The other two sections of her class have 29 and 35. Each is close to 30 or a little more, so she estimates the whole class has about 100 children. (Exactly: 32 + 29 + 35 = 96. Very close!)

Her school also has Classes 7, 8, 9 and 10, each with 3 sections. So there are 5 classes (6 to 10). If each has about 100 children, the school has about 5 × 100 = 500 students.

A sensible estimate is close to the real number. To check one, round to easy numbers, work it out quickly, and see if the answer is near. An estimate of 5000 students for Paromita's school would not be sensible: it is ten times too big.