a car distance rate and time questions?

Question

A car leaves Sacremento for LA traveling 54mi/hr. A half hour later another car leaves Sacremento for LA traveling 64 mi/hr. How long after the second car leaves will it pass the first car?

Answer 1

d=r*t

d=54*t

d=64*(t-0.5)

equate the d's

54t=64*(t-0.5)

54t=64t-32

54t-64t=-32

-10t=-32

10t=32

t=32/10

t=3.2 hours (answer)

check:54*3.2=172.8 miles

         64*(3.2-0.5)=64*2.7=172.8 miles