Linear Equations in Two Variables

SAT Math· difficulty 5/5

A boat goes 20 mi downstream in 2 h and returns in 4 h. Boat speed in still water:

  • A

    1010 mph

  • B

    6.56.5 mph

  • C

    55 mph

  • D

    7.57.5 mph

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Explanation

b+c=10b + c = 10, bc=5b - c = 5; b=7.5b = 7.5.

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