Answer:
The rate of the boat is 75.17 km/h and the rate of the stream is 17.83 km/h
Step-by-step explanation:
System of Equations
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:
[tex]\displaystyle B-S=\frac{172}{3}[/tex]
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:
[tex]\displaystyle B+S=\frac{372}{4}=93[/tex]
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:
[tex]S = \frac{107}{6}\approx 17.83\ km/h[/tex]
From [2]:
[tex]B = 93 - \frac{107}{6}[/tex]
[tex]B=\frac{451}{6}\approx 75.17\ km/h[/tex]
