Question:
The population of a certain city was 72000 on the last day of the year 1998. During next year it increased by 7% but due to an epidemic it decreased by 10% in the following year. What was its population at the end of the year 2000?
Solution:
Population at the end of the year $2000=\mathrm{P}\left(1+\frac{\mathrm{R}_{1}}{100}\right)\left(1-\frac{\mathrm{R}_{2}}{100}\right)$
$=72,000\left(1+\frac{7}{100}\right)\left(1-\frac{10}{100}\right)$
$=72,000(1.07)(0.9)$
$=69,336$
Thus, the population at the end of the year 2000 was 69,336 .
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