abdulfmk wrote:

Xavier starts from P towards Q at a speed of 30 kmph and after every 12 mins increases his speed by 5 kmph. If the distance between P and Q is 51km, then how much time does he take to cover the distance?

A) 60 mins

B) 72 mins

C) 90 mins

D) 120mins

E) 100mins

Distance traveled by xavier in the initial 12 minutes = 30(12/60) =6

after these initial 12 minutes, xavier increases his speed by 5 km/h, thus his new speed becomes 35 km/h

now distance traveled in next 12 minutes = 35(12/60) = 7

now, his new speed becomes 40km/h, therefore distance traveled in 12 min. with this speed = 40(12/60) =8

as we can see that after every 12 minutes distance traveled by xavier increases by 1 unit, therefore instead of calculating the distance covered in every 12 minutes we can just simply add the distance from 6 onward and can stop when the sum becomes 53.

thus we have 6+7+8+9+10+11 =53, as the number of values used to make this sum a total of 53 is 6. hence total time taken = 12.(6) = 72 minutes.