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Using the boat problem (30 km each way, stream 2 km/h, total time 8 h), the speed of the boat in still water (km/h) is:

Class 10Quadratic Word ProblemsAlgebra — Quadratics

A7
B16
C9
D8

Step-by-Step Solution

\frac{30}{x - 2} + \frac{30}{x + 2} = 8. \frac{30 ( 2 x )}{x ^{2} - 4} = 8, 60 x = 8 (x^{2} - 4), 8 x^{2} - 60 x - 32 = 0, 2 x^{2} - 15 x - 8 = 0, (2 x + 1) (x - 8) = 0. x = 8 km / h

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Answer: D) 8

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