Question

A biologist who has been studying herd movements in elephants just finished spending
several hours with the herd. The elephants are now moving due east at 3 miles per hour. The
biologist, meanwhile, is driving due west to base camp at a rate of at 25 miles per hour. In
how long will the biologist be 1 mile from the herd?
If necessary, round your answer to the nearest minute.

Answer 1

We have been given that the speed of elephants is 5km/h east and his speed is 41km/h west.
We have to find after how long will he be 13km from the herd.
Since the biologist is going to the west and the elephants towards east, their relative speed will be calculated by adding their respective speeds.
So final their relative speed will be:
= 5 km/h + 41 km/h
= 46 km/h
Now we want their distance to be 13 km and we have calculated relative speed as 46 km/h.
So using formula :
Speed = Distance / Time,
We calculate time as :
= Distance / Speed
= 13 / 46
= 0.28 hours
= 16.8 minutes.
So after 16.8 minutes, biologist will be 13 km away from the herd.