Question

A person wishes to reach his destination $90$ km away in three hour but for the first half of the journey his speed was $20$ km/hr. His average speed for the rest of the journey should be

• A. $40$ km/hr
• B. $0.75$ km/min
• C. $1$ km/min
• D. $65$ km/hr

Answer 1

The correct option is C $1$ km/min

Time taken to travel the first half of the journey $=\frac{45}{20}hrs=\frac{9}{4}hrs$

Total time $=$ 3 hrs

$\therefore$ Time left for the second half of the journey $=(3-\frac{9}{4})hrs=\frac{3}{4}hrs$

Distance to be covered = 45 km

$\therefore$ Required speed $=\frac{45}{\frac{3}{4}}km/hr$

$=60km/hr=1km/min$