Question 460300
A car was driven for 2 hours part of the time at 40 miles per hour and the rest of the time at 60 miles per hour.
 the total distance was 90 miles . how long did the car travel at each speed.
:
Let x = distance at 40 mph
then
(90-x) = distance at 60 mph
:
Write a time equation; time = dist/speed
:
4o mph time + 60 mph time = 2 hrs
{{{x/40}}} + {{{((90-x))/60}}} = 2 
Multiply by 120
120*{{{x/40}}} + 120*{{{((90-x))/60}}} = 120(2)
Cancel the denominators and you have:
3x + 2(90-x) = 240
3x + 180 - 2x = 240
3x - 2x = 240 - 180
x = 60 mi at 40 mph
then
90-60 = 30 mi at 60 mph
:
Find the times at each speed
60/40 = 1.5 hr at 40 mph
30/60 = .5 hrs at 60 mph
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total 2 hrs