Question 284297: Fred and Desi left Steamtown Mall at 9:00 am and began walking in opposite directions. At 1:00 pm that same day they were 20 miles apart. If Fred walks 0.5 mph slower than Desi, what is Desi's speed of walking?
A. 2.25 mph B. 2.75 mph C. 3.5 mph D. 5 mph E. None of these.
Found 4 solutions by mananth, ikleyn, josgarithmetic, mccravyedwin:
Answer by mananth(16949)   (Show Source):
You can put this solution on YOUR website! let desi's speed be x mph
Fred's speed = x-0.5mph
In 5 hours desi has walked 5x miles
In 5 hours fred has walked 5(x-0.5) miles = 5x-2.5
5x+5x-2.5 = 20
10x=17.5
x=7.5 mph Desi's speed
Fred's speed will be 7 mph
Answer by ikleyn(53750)  (Show Source):
You can put this solution on YOUR website! .
Fred and Desi left Steamtown Mall at 9:00 am and began walking in opposite directions.
At 1:00 pm that same day they were 20 miles apart. If Fred walks 0.5 mph slower than Desi,
what is Desi' speed of walking?
A. 2.25 mph B. 2.75 mph C. 3.5 mph D. 5 mph E. None of these.
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In the post by @mananth, the treatment is not adequate to the problem.
Due to this reason, the solution and the answer are incorrect.
I came to bring a correct solution.
let desi's speed be x mph
Fred's speed = x-0.5 mph
In 4 hours Desi has walked 4x miles
In 4 hours Fred has walked 4(x-0.5) miles = 4x-2
4x + (4x -2) = 20
8x = 22
x =  =  = 2.75 mph Desi' speed <<<---=== ANSWER
CHECK. The distance apart in 4 hours, at 1:00 pm, is 4*2.75 + 4*(2.75 - 0.5) = 20 miles. ! Precisely correct !
Solved correctly.
Answer by josgarithmetic(39792)  (Show Source):
Answer by mccravyedwin(421)  (Show Source):
You can put this solution on YOUR website!
Let Desi's speed be R, then Fred's speed is then R-0.5
Their speed of separation is the sum of their speeds or R+R-0.5 or 2R-0.5
From 9:00 am to 1:00 pm is 4 hours.
Distance = Rate x Time
20 = (2R-0.5)T
20 = (2R-0.5)(4)
20 = 8R-2
22 = 8R
22/8 = R
2.75 = R
Answer: Desi's speed of walking is 2.75 mph
Edwin
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