SOLUTION: By increasing his average speed by 10 mi/hr, a motorist could save 36 minutes in traveling a distance of 120 miles. Find her actual average speed.

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Question 481055: By increasing his average speed by 10 mi/hr, a motorist could save 36 minutes in traveling a distance of 120 miles. Find her actual average speed.
Answer by jorel1380(3719) About Me  (Show Source):
You can put this solution on YOUR website!
120/p=120/(p+10)+36/60
120/p=120/(p+10)+.6
1200/p=1200/(p+10)+6
1200(p+10)=1200p+6p2+60p
1200p+12000=1200p+6p2+60p
6p2+60p-12000=0
p2+10p-2000=0
(p+50)(p-40)=0
p=40 or -50
Throwing out the negative answer, we get the motorist's actual average speed to be 40 mph..