Question

At 9 am a car (A) began journey from a point, traveling at 40 mph. At 10 am another car (B) started traveling from the same point at 60 mph in the same direction as car (A). At what time will car B pass car A?

Answer 1

When car B passes car A, they will have traveled the same distance, d.

speed = distance/time

distance = speed * time

Car A travels t time.
Since car B starts an hour later, car B travels t - 1 time.

Car A:
d = st
s = 40t

Car B:
d = st
d = 60(t - 1)

The distance are equal, so

40t = 60(t - 1)

40t = 60t - 60

-20t = -60

t = 3

Car A started at 9 am.
9 am + 3 hours = noon.

Answer: at noon.