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Question

On a weekend outing, Charles rents a motorboat for 6 hours to travel down the river and back. The rental operator tells him to go for 2 hours downstream, leaving 4 hours to return upstream.

 

If the river current flows at a speed of 7 mph, how fast must CharlesCharles travel in order to return in 6 hours?

How far downstream did Charles go before he turned back?

 

Answer 1

d=r*t

d=(r+7)*2

d=(r-7)*4

2(r+7)=4(r-7)

2r+14=4r-28

28+14=4r-2r

42=2r

r=21 mph must be Charles' rate

d=(21+7)*2=28*2=56 miles

d=(21-7)*4=14*4=56 miles