Estimating products

In your book, Maths Mela (Chapter 6, The Dairy Farm), we estimate products. To estimate means to find a number that is close to the answer, quickly, without working it out exactly. We round each number to a nearby easy number and multiply those.

25 × 31: 31 is close to 30, and 25 × 30 = 750. So 25 × 31 is about 750. (The exact answer is 775, just one more 25.) 132 × 19: 132 is close to 130 and 19 is close to 20, and 130 × 20 = 2,600. So 132 × 19 is about 2,600.

248 × 49: 248 is close to 250 and 49 is close to 50. 250 × 50 = 12,500, so 248 × 49 is about 12,500. 101 × 11: 101 is close to 100 and 11 is close to 10, and 100 × 10 = 1,000. So 101 × 11 is about 1,000. And 12 × 25 needs no rounding at all: it is exactly 300.

An estimate is not the exact answer, but it tells us how big the answer should be. If someone says 248 × 49 is 1,215, we know at once that it is far too small, because the answer should be near 12,500.