Go the extra mile and answer today’s practice question. Click here for the answer and explanation.

Guard A with a speed of 3 mph and guard B with a speed of 2 mph will cross each other the first time when A has covered 3 miles and B has covered 2 miles, i.e. in 1 hour. Then guard A will continue and cover 2 miles, turn around and cover 1 mile back in the next hour while guard B will cover 2 miles in this time.

Now in the 3rd hour, guard A will cover 3 miles, and B will cover 1 mile, turn around and cover 1 more mile. Guard B will cross guard A at the end of the 3rd hour. So the total distance covered by both = distance covered by guard A + distance covered by guard B

= (3 + 2 + 1 + 3) + (2 + 2 + 1 + 1) = 15 miles.

D is the correct answer.