Question:
Tick (✓) the correct answer:
The annual rate of growth in population of a town is 10%. If its present population is 33275, what was it 3 years ago?
(a) 25000
(b) 27500
(c) 30000
(d) 26000
Solution:
(a) 25000
Let $P$ be the popultion 3 years ago.
Now, present population $=33275$
$\Rightarrow 33275=P \times\left(1+\frac{10}{100}\right)^{3}$
$\Rightarrow 33275=P \times\left(\frac{110}{100}\right)^{3}$
$\Rightarrow 33275=P \times\left(\frac{11}{10}\right) \times\left(\frac{11}{10}\right) \times\left(\frac{11}{10}\right)$
$\Rightarrow 33275=\frac{1331 P}{1000}$
$\therefore P=\frac{33275 \times 1000}{1331}=25000$