Q.19: Leaving home at the same time, Amal reaches office at 10:15 am if he travels at 8kmph, and at 9:40 am if he travels at 15kmph. Leaving home at 9:10 am, at what speed, in kmph, must he travel so as to reach office exactly at 10:00 am?
Correct Answer: 12
Speed are 8 km/hr and 15 km/hr
So it takes 15t times and 8t times
Difference of times = 15t – 8t = 7t
7t = 35 minutes (10:15 min – 9:40 min)
t = 5 minutes
He takes 75 minutes by travelling at 8 km/hr and 40 minutes if travelled at 15 km/hr
He starts at 9 am.
So, 9:10 to 10:00 = 50 minutes
15 km/hr = 40 min
And at what speed he should travel, so as to reach there within 50 minutes
15×40 / 50 = 12 km/hr