Two cars A and B started from point X & Y respectively, and the distance between these two points is 660 km. Both cars started at 10 AM and meet at 3 PM. If speed of car A is 12 km/hr more than that of B, then find the speed of car A (in km/hr)?

Correct option is B

Information Given:

Distance between X and Y = 660 km

Both cars started at 10 AM and meet at 3 PM (so, time taken = 5 hours)

Speed of A is 12 km/hr more than speed of B

Concept/Formula:

Relative Speed when moving towards each other (opposite directions) = Speed of A + Speed of B

Distance = Relative Speed × Time

Let speed of B = x km/hr, so speed of A = x + 12 km/hr

Explanation:

Total time taken to meet = 5 hours

So, (x + x + 12) × 5 = 660

(2x + 12) × 5 = 660

2x + 12 = 132

2x = 120

x = 60

Speed of A = x + 12 = 60 + 12 = 72 km/hr

Short Trick:

Sum speeds = 660/5 = 132

So, 2x + 12 = 132 (x is speed of car B)

x + 6 = 66

x = 60

Speed of A = 72 km/hr