Question

A remote-control car races straight down the street at 15 feet per second. Four seconds later, a second remote-control car races straight down the same street at 25 feet per second. How long will it take the second car to catch up to the first car?

A remote-control car races straight down the street at 15 feet per second. Four seconds later, a second remote-control car races straight down the same street at 25 feet per second. How long will it take the second car to catch up to the first car?

@Mathematics

Answer 1

15 x 4 = 60 feet (total head start)
60 / 25 = 2.4 sec (total head start / 2nd car speed)
15 x 2.4 = 36 feet (additional feet gained by 1st car while 2nd car makes up 60 feet)
36 + 60 = 96 feet (additonal feet + headstart)
96 / 25 = 3.84 sec (Total feet / 2nd car speed)
3.84 + 4 = 7.84 (additional time + headstart)

My answer is 7.84 sec

Answer 2

Solve as an equation, where distance travelled by first car=distance travelled by second car:

15*4+ 15x=25x (Where x is the number of seconds after the second car starts).
10x=60, which gives x=6 seconds