Using the average decadal growth rate from the table, which option is the…

Concept

A decade-to-decade population growth rate is calculated as (new population − old population) ÷ old population × 100%.

For several decades, the average decadal growth rate is the arithmetic mean of the individual percentage rates. A one-decade projection multiplies the latest population by (1 + average rate ÷ 100).

Application

1. For 1951–1961: (21 − 20) ÷ 20 × 100 = 5.00%. For 1961–1971: (24 − 21) ÷ 21 × 100 ≈ 14.29%.

2. For 1971–1981: (27 − 24) ÷ 24 × 100 = 12.50%. For 1981–1991: (30 − 27) ÷ 27 × 100 ≈ 11.11%.

3. For 1991–2001: (32 − 30) ÷ 30 × 100 ≈ 6.67%. For 2001–2011: (35 − 32) ÷ 32 × 100 = 9.375%.

4. Average rate = (5.00 + 14.29 + 12.50 + 11.11 + 6.67 + 9.375) ÷ 6 ≈ 9.823%.

5. Projected population in 2021 = 35 × (1 + 9.823 ÷ 100) ≈ 38.44 million.

Cross-check

About 9.823% of 35 million is 3.438 million; adding it to 35 million gives 38.438 million. Among the offered values, 38.49 million is the nearest estimate, differing by only about 0.052 million.

Therefore, the estimated population in 2021 is about 38.44 million, so the offered value 38.49 million is selected.