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Serggg [28]
3 years ago
12

A motorboat travels 172 km in 3 hours going upstream and 372 in 4 hours going downstream. What is the rate of the boat in still

water and what is the rate of the current?
Mathematics
1 answer:
torisob [31]3 years ago
4 0

Answer:

<em>The rate of the boat is 75.17 km/h and the rate of the stream is 17.83 km/h</em>

Step-by-step explanation:

<u>System of Equations</u>

Let's call:

B = speed (rate) of the boat in still water

S = speed (rate) of the stream

The boat travels 172 km in 3 hours when going upstream, that is when the speed of the stream subtracts its own speed. The speed is the distance divided by the time, thus:

\displaystyle B-S=\frac{172}{3}

Multiplying by 3:

3B - 3S = 172        [1]

The boat travels 372 km in 4 hours downstream when the speed of the current adds to its own:

\displaystyle B+S=\frac{372}{4}=93

B + S = 93

Solving for B:

B = 93 - S       [2]

Substituting in [1]

3(93 - S) - 3S = 172

Operating:

279 - 3S - 3S = 172

279 - 6S = 172

Subtracting 279:

- 6S = 172 - 279

- 6S = -107

Multiplying by -1 and solving for S:

S = \frac{107}{6}\approx 17.83\ km/h

From [2]:

B = 93 - \frac{107}{6}

B=\frac{451}{6}\approx 75.17\ km/h

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