Question 258735: An airplane flew for 8 hours at an air speed of x miles per hour (mph), and for 7 more hours at 325 mph. If the average airspeed for the entire flight was 350 mph, which of the following equations could be used to find x ?
A. x + 325 = 2(350)
B. x + 7(325) = 15(350)
C. 8x – 7(325) = 350
D. 8x + 7(325) = 2(350)
E 8x + 7(325) = 15(350)
Answer by Theo(13342)   (Show Source):
You can put this solution on YOUR website! An airplane flew for 8 hours at an air speed of x miles per hour (mph), and for 7 more hours at 325 mph. If the average airspeed for the entire flight was 350 mph, which of the following equations could be used to find x ?
general formula is rate * time = distance.
let r = rate
let h = time in hours
let d = distance
total time it took was 8 + 7 = 15 hours.
average speed for the whole flight was 350 miles per hour.
formula for the entire flight becomes:
350 * 15 = d
formula for the first leg of the trip is equal to:
x * 8 = d1 where d1 is the distance flown for the first leg of the trip.
formula for the second leg of the trip is equal to :
325 * 7 = d2 where d2 is the distance flown for the second leg of the trip.
since we know that d1 + d2 = d, then we have a general formula that states
x * 8 + 325 * 7 = 350 * 15
that looks very much like selection E which is:
8x + 7(325) = 15(350)
your answer is selection E.
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