AAPL wrote:Marcia took a trip consisting of three segments at three different speeds: she drove a distance of (5D) at a speed of (2v), then a distance of (4D) at a speed of (3v), then a distance of D at a speed of (6v). In terms of D & v, what was the total time of Marcia’s trip?
A) (4D)/v
B) (4v)/D
C) (10D)/(11v)
D) (10v)/(11D)
E) (11D)/(10v)
Let v = 1 mph and D = 6 miles.
Time to travel 5D miles at a speed of 2v mph = d/r = (5*6)/(2*1) = 15 hours.
Time to travel 4D miles at a speed of 3v mph = d/r = (4*6)/(3*1) = 8 hours.
Time to travel D miles at a speed of 6v mph = d/r = 6/(6*1) = 1 hour.
Total time = 15+8+1 = 24 hours.
The target value is 24 hours.
Now plug v=1 and D=6 into the answers to see which yields the target value.
Only
A works:
(4D)/v = (4*6)/1 = 24.
The correct answer is
A.
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