Question

Use rounding to the nearest whole number and clustering to give an estimate for: 15.23 + 12.8 + 4.93 + 7.21.
A. 42
B. 41
C. 40

Answer 1

15.23, when rounded to the nearest whole number, becomes 15.
12.8 becomes 13.
4.93 is 5
and 7.21 is 7.
So 15+13+5+7 is 40 (C).

It's worth noting that if you just look at the decimal values, in this question they somewhat "fit together". (.23+.8=1 and .93+.21= around 1). This means the estimate will be closer to the real sum than otherwise.