Two places—P and Q are 400 miles apart. A car starts from P at a speed of 50 mph towards Q. After 75 minutes, another car starts from Q to P at a speed of 40 mph. At what time will the cars meet?

ANS: 3 hr and 45 mins

The distance between the points P and Q is 400 miles.

Car A (say) starts to move from P towards Q at a speed of 50 mph.

Hence, after 75 mins i.e. 1.25 hours, it will cover a distance 

=Speed×time=  50×1.25 =62.5 miles.

Since, after 75 mins another car B (say) starts to move from Q towards P at a speed of 40 mph.

Hence, the remaining (400-62.5) =337.5 miles will be covered by both Car A and Car B with a combined speed of (50+40)= 90 mph.{opposite directing speed add}

$$time=\frac{Distance}{speed}$$

$$time=\frac{337.5}{90}$$

$$time=3.75$$

Therefore, they will take =3.75 hr. or 3 hr and 45 mins more to meet each other.