i tried many times to solve this but i cant seem to do it...help?
correct answer: 49.5
A man drove to the beach at an average speed of 55 mi/h and returned home over the same route at the average speed of 45 mi/h. It took him 2 hours longer on the return trip. What was his average speed?
2006-09-04 14:01:09 · 4 answers · asked by ☆----|| 。。¤ ¥ ąйGel ♥ ♀♂。。||---- 2 in Science & Mathematics ➔ Mathematics
d=distance
t=time
55 * t = d
45 (t + 2) = d
55t=45t +90
10t = 90
t = 9
(9/20)*55 + (11/20)*45 = weighted average
NOTE: The 20 is the total time in hours (t + t + 2)
WA = 49.5
2006-09-04 14:13:07 · answer #1 · answered by Slider728 6 · 0⤊ 0⤋
d/55 = d/45 -2
d/55=(d-90)/45
45d = 55d - 4950
10d = 4950
d=495 miles
it took him 9 hours to go
it took him 11 hours to return
20 hours for 990 miles
average = 49.5 miles per hour
2006-09-04 21:14:53 · answer #2 · answered by bob h 3 · 0⤊ 1⤋
HINT it has to do with the fact that he spends MORE TIME at one speed than the other --------what you are solving for is the TIME SPENT AT EACH SPEED you know the average speed ! take your time i will be back ! WELL I WAITED TOO LONG i see you have the solutions BUT DID YOU EVER SOLVE IT ?
2006-09-04 21:08:56 · answer #3 · answered by Anonymous · 0⤊ 1⤋
48 is the correct answer
and dont ask me how i got it
2006-09-04 21:06:28 · answer #4 · answered by Mr. KnowItAll 1 · 0⤊ 2⤋