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Sagot :
9514 1404 393
Answer:
- 50 mph for 4.8 hours
- 60 mph for 1.2 hours
Step-by-step explanation:
One way to write the relationship between time, speed, and distance is ...
time = distance/speed
For the first part of the trip, the time is ...
t1 = 240/r
For the second part of the trip, the time is ...
t2 = 72/(r+10)
The total time is 6 hours, so we have ...
t1 +t2 = 6
240/r +72/(r+10) = 6
We can simplify this a bit by multiplying by (r)(r+10)/6 to get ...
40(r+10) +12(r) = r(r+10)
r² -42r -400 = 0 . . . . . . . . subtract the left side and collect terms
(r -50)(r +8) = 0 . . . . . . . . factor
r = 50 . . . . . the positive solution of interest.
The two average speeds were 50 mph and 60 mph.
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