Evaluate $\frac{21}{9}$ to 3 significant figures

Analyze the question: You need to divide 21 by 9 and round the result to 3 significant figures.

Concept: Significant figures are counted from the first non-zero digit. For 3 s.f., keep three digits and round using the fourth digit. If the fourth digit is 5 or more, round the third digit up. If it is less than 5, leave it as it is.

Solution:

1. Simplify the fraction: 21/9 = 7/3
2. Divide: 7 ÷ 3 = 2.3333...
3. The first three significant figures are 2, 3, 3. The fourth digit is 3, which is less than 5, so we do not round up.

21/9 = 2.33 (to 3 s.f.)

Answer: The correct option is D. 2.33.

Tip: Simplify the fraction first (21/9 = 7/3). Recurring decimals like 2.333... are common in JAMB. For 3 s.f., look only at the 4th digit to decide whether to round. Also, 2.30 and 2.31 are far from 2.333, so you can eliminate them quickly.