Question

Two cars are traveling in the same direction. The first car is going 40mph, and the second car is going 55 mph. The first car left 3 hours before the second car. Which equation could you use to find how many hours it will take for the second car to catch up to the first car? hint: how many miles has the first car gone in those 3 hours?

Answer 1

Assuming both cars start at the same position, in the first 3 hours the first car covers a distance of

(40 mi/h) (3 h) = 120 mi

Take the 3 hour mark to be the origin, so that the first car's position after t hours is

120 mi + (40 mi/h) t

while the second car's position is

(55 mi/h) t

The second car catches up to the first when their positions are equal:

120 mi + (40 mi/h) t = (55 mi/h) t

120 mi = (15 mi/h) t

t = (120 mi) / (15 mi/h)

t = 8 h