Question 104674
During rush hour, Bill can drive 15 miles using the side roads in the same time that it takes to travel 10 miles on the freeway. If Bill's rate on the side roads is 8 mi/h faster than his rate on the freeway, find his rate on the side roads.
:
Let s = speed on the side roads
then
(s-8) = speed on the freeway
:
They tell us the times are equal so make a time equation: Time = Dist/speed
:
Sideroad time = freeway time
{{{15/s}}} = {{{10/((s-8))}}}
:
Cross multiply:
15(s-8) = 10s
15s - 120 = 10s
15s - 10s = +120
s = 120/5
s = 24 mph his speed on the side roads
:
:
Check solution by finding if the times are equal:
15/24 = .625
10/16 = .625
:
How about this? Did it make sense to you?