Question

A person wishes to reach his destination $90$ km away in $3$ hours, but for the first half of the journey, his speed was $20$ km/hr. His average speed for the rest of the journey is

• A. $1$ km/hr
• B. $0.5$ km/min
• C. $1$ km/min
• D. $0.5$ km/hr

Answer 1

The correct option is C $1$ km/min

Time taken to travel $45$ km $=\frac{45}{20}=\frac{9}{4}=2$ hrs $15$ min.
$\therefore$ Remaining time
$=(3\text{hrs}-2\text{hrs}15\text{min})=45$ min
Hence, required average speed for the rest $45$ km $=\frac{45}{45}=1$ km/min