Question 98632
: During rush hour, Fernando can drive 40 miles using the side roads in the same time that it takes to travel 30 miles on the freeway. If Fernando's rate on the side roads is 7 mi/h faster than his rate on the freeway, find his rate on the side roads.
:
Let s = speed on the side-road
then
(s-7) = speed on the freeway
:
Time = dist/speed
:
Side-road time = Freeway time
{{{40/s}}} = {{{30/((s-7))}}}
:
Cross multiply and you have:
40(s-7) = 30s
40s - 280 = 30s
40s - 30s = +280
10s = 280
s = 280/10
s = 28 mph on the side-roads
:
:
Check our solution by finding the times, they should be equal
40/28 = 1.42857
30/21 = 1.42857, confirms our solution
:
Did this help? Not that hard, right?