Question

Two buses, P and Q left town A for town B at an interval of 15 minutes and with a uniform speed of 60 km/h. What was the speed
of another bus R bound for town A from town B if it met the first two buses at an interval of 9 minutes? [Assuming the speed of
bus R was uniform]
A 30 km/h
b)40 km/h
c)50 km/h
d)80 km/h​

Answer 1

Answer:

Option B answer is 40 km/h

Explanation:

1st we need to understand the directions of the buses.

bus P and bus Q are moving in same direction with equal distance as both have uniform speed and bus Q left after 15 mints.  so bus Q is 15 km behind .

speed of bus P and Q = 60km/h

distance covered in 1 mint = 60 km/h/ 60 = 1km/min

total distance covered in 15 mints= 1 x 15 = 15 km

so both P and Q are 15 km apart.

now bus R is moving in opposite direction so the speed will add up .

we have the time between bus R passes bus P and Q that is 9 mint

As we know that the distance between Bus P and Q is 15km.

And R took 9 mints to cover 15 km from this we will calculate the speed of bus R

Speed =15 /9 min= 1.66 km/min

if we convert it in km/h it will be = 1.66 km/min * 60= 99.99km/h or (100Km/h)

as we know that both buses are in opposite direction and moving so speed will add up . this is the relative speed of both buses.

we know the speed of bus P and Q so we will subtract the speed form total speed to find the actual speed of bus R

100km/h- 60km/h = 40km/h

which is the correct answer.