Question

Explain how you could estimate 22%
of 78
to check if your answer is reasonable.



WRITER

Answer 1

A few quick estimation methods you can use to check your answer:

1. Use 10% chunks:
- 10% of 78 = 7.8, so 20% = 2×7.8 = 15.6.
- 2% = 0.2×7.8 = 1.56.
- So 22% = 15.6 + 1.56 = 17.16 → the exact value, but done with simple parts.

2. Round to easy numbers for a quick check:
- Round 22% to 20% and 78 to 80: 20% of 80 = 0.2×80 = 16. So your true answer should be near 16 (and indeed 17.16 is close).

3. Use an upper/lower bound:
- 25% of 78 = 19.5 (upper bound), 20% = 15.6 (lower bound) ⇒ 22% must be between about 15.6 and 19.5.

So if your answer is around 17 (or at least between ~16 and ~19), it’s reasonable.