Sarang B.

asked • 05/07/21# help me quickly on this question

Kenny can swim 30 meters downstream in the same amount of time it takes him to swim 15 meters upstream. If Kenny can swim 3 4meters per second in still water, then what is the rate of the current, and how long does it take him to swim 30 meters downstream?

## 1 Expert Answer

Pranav M. answered • 05/08/21

Math Tutor Specializing in Elementary Math, Algebra, and SAT Math

Let t = the time in seconds it takes for Kenny to swim 30 meters downstream = the time it takes him to swim 15 meters upstream. The unit of t is seconds (s).

Let x = the rate of the current. The unit of x is meters per second (m/s).

Since the current helps him when he is swimming downstream, we can add the rate of the current to Kenny's swimming rate in still water. Then, we can multiply this by t, as it will take Kenny this long to swim 30 meters downstream.

Downstream Equation: (3/4 + x)*t = 30

Since the current works against him when he is swimming upstream, we can subtract the rate of the current to Kenny's swimming rate in still water. Then, we can multiply this by t, as it will take Kenny this long to swim 15 meters upstream.

Upstream Equation: (3/4 - x)*t = 15

Then, solve the equations.

0.75t + xt = 30

0.75t - xt = 15

1.5t = 45

t = 30 seconds

Plug t into either equation, I will use the downstream equation.

0.75 * (30) + 30x = 30

22.5 + 30x = 30

30x = 7.5

x=0.25 m/s

Therefore, the rate of the current is 1/4 m/s and it will take Kenny 30 seconds to swim 30 meters downstream.

Be careful not to forget to put units when writing your answer.

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Philip P.

Why do you need the answer quickly? Is this a test question?05/08/21