algebra problem please help?

Bill can row 3mph in still water. It takes him 3hrs36 minutes to go 3 miles upstream and return. Find the speed of the current

Comments

  • Let x = speed of the current.

    Speed = distance/time so time = distance/speed

    upstream time + downstream time = 3.6 hours

    3/(3 - x) + 3(3 + x) = 3.6

    3(3+x) + 3(3-x) = 3.6(3-x)(3+x)

    9 + 3x + 9 - 3x = 3.6(9 - x^2)

    18 = 3.6(9-x^2)

    5 = 9 - x^2

    x^2 = 4

    x = 2

    The speed of the current was 2 mph

    Check:

    3 - 2 or 1 mph for 3 miles upstream = 3 hours time

    3 + 2 or 5 mph for 3 miles downstream = .6 hours or 36 minutes

    so total time would be 3 hours 36 minutes

    Jim

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