Question

$\text{The population of a city doubles in every 10}\text{years. If the initial population was}\frac{3}{20}\text{million,}\text{calculate the population after 30 years .}$

• A. $\frac{3}{10}\text{million}$
• B. $\frac{6}{5}\text{million}$
• C. $\frac{3}{5}\text{million}$
• D. $\frac{9}{2}\text{million}$

Answer 1

The correct option is B $\frac{6}{5}\text{million}$

$\text{Initial population}=\frac{3}{20}\text{million}$

$\text{The population}doubles\text{every 10 years}$

$\therefore \text{Total population after 10 years:}=(\frac{3}{20}\times 2)\text{million}$

$=\frac{3}{20}\times 2$

$=\frac{3\times 2}{20\times 1}$

$=\frac{6}{20}$

$=\frac{6÷2}{20÷2}$

$=\frac{3}{10}\text{million}$

$\text{Total population after 20 years:}$

$=(\frac{3}{10}\times 2)\text{million}$

$=\frac{3}{10}\times 2$

$=\frac{3\times 2}{10\times 1}$

$=\frac{6}{10}\text{million}$

$\text{Total population after 30 years:}$

​​​​​​​$=(\frac{6}{10}\times 2)\text{million}$

​​​​​​​$=\frac{6\times 2}{10\times 1}$

​​​​​​​$=\frac{12}{10}$

​​​​​​​$=\frac{6}{5}\text{million}$

$\therefore \text{The population of the city after 30}\text{years is}\frac{6}{5}\text{million}$