Question

The population of an invasive species of moth doubles every $5$ years. If the initial population is $300$, what will be the population after $15$ years?

• A. $900$
• B. $1200$
• C. $2000$
• D. $2400$

Answer 1

The correct option is D $2400$

Population of an invasive species of moth doubles every $5$ years.

Let the initial population be $x$

So after $5$ years, population will be $2\times x=2x$

After $10$ years, population will be $2\times 2x=4x$

After $15$ years, population will be $2\times 4x=8x.$

Here, initial population is $x=300$.

After $15$ years, population will be $8x=8\times 300=2400$

Hence, the population after $15$ years is $2400$