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Question 1085268: Ed is a runner and he runs a 8 km loop every day. The first 4 km, he
runs at 12km/hr. He runs much slower on the way home. If it takes him 1 hour in total to
run the loop, how fast is he running for the last 4 km?
Answer by jim_thompson5910(35256)   (Show Source):
You can put this solution on YOUR website! The formula we'll use here is
d = r*t
where,
d = distance
r = rate (aka speed)
t = time
If Ed runs 4 km and his speed is 12 km/hr, then d = 4 and r = 12. Plug these values into the formula above and solve for t
d = r*t
4 = 12*t
4/12 = 12*t/12
1/3 = t
t = 1/3
So it takes Ed 1/3 of an hour, which is (1/3)*60 = 20 minutes to run the 4 km.
20 minutes pass by when Ed runs the first 4 km, leaving 60 - 20 = 40 minutes left over.
40 minutes = 40*(1/60) = 40/60 = 4/6 = 2/3 of an hour
So we'll use t = 2/3 and d = 4 to find the rate (r)
d = r*t
4 = r*(2/3)
3*4 = 3*r*(2/3) ... multiply both sides by 3
12 = 2r
2r = 12
2r/2 = 12/2 ... divide both sides by 2
r = 6
Therefore, Ed's speed on the last four kilometers is 6 km/hr which is the final answer.
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