Question

A boat starts with the speed of $1km$ per hour. After every $1km$, the speed of the boat becomes twice. How much will be the average speed of the boat at the end of journey of $2.5km$?

• A. $\frac{2.5}{1.5125}$
• B. $\frac{2.5}{1.75}$
• C. $\frac{2.5}{1.625}$
• D. $\frac{2.5}{1.50}$

Answer 1

The correct option is B $\frac{2.5}{1.75}$

For first $1km$, boat takes one hour.

After $1km$ the speed becomes double i.e. $2km$ per hour.

So, in next half an hour the boat will cover next $1km$.

And to cover a distance next $0.5km$, it takes one fourth of the hour i.e. $0.25$ hour.

After covering $1km$, the boat will cover next $1.5km$ in $0.75$ hour.

Thus, the average speed of the boat at the end will be $\frac{2.5}{1.75}$.

Hence, option B is correct.