# The speed of crew in still water. ### Precalculus: Mathematics for Calcu...

6th Edition
Stewart + 5 others
Publisher: Cengage Learning
ISBN: 9780840068071 ### Precalculus: Mathematics for Calcu...

6th Edition
Stewart + 5 others
Publisher: Cengage Learning
ISBN: 9780840068071

#### Solutions

Chapter 1.6, Problem 73E
To determine

## To find: The speed of crew in still water.

Expert Solution

The speed of crew in still water is 6 km.

### Explanation of Solution

Given:

A crew takes 2 h 40 min to row 6 km upstream and downstream.

The rate of flow of the stream is 3 km/h.

Formula used:

Distance formula is,

distance=time×rate

Calculation:

Let the speed of crew be x.

Tabulate the given information into the language of algebra.

 Distance Speed Time Upstream 6 x−3 6x−3 Downstream 6 x+3 6x+3

Model the equation for the above information.

upstreamtime+downstreamtime=totaltime6x3+6x+3=83

Simplify the above equation for x,

18(x+3)+18(x3)=8(x3)(x+3)(Multiplyby3(x3)(x+3))18x+54+18x54=8(x29)36x=8x2728x236x72=0

Factor the above equation.

(x6)(2x+3)=0x=6,x=32

The speed cannot be negative, so the speed of crew is 6 km.

Thus, the speed of crew in still water is 6 km.

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