Bonjour,
En ces temps de disette de problèmes,
aidez-moi à rédiger en Anglais la résolution de ce casse-tête:
"The current in a stream moves at a rate of 7 mph. If a boat travels 98 miles downstream in the same time that it takes to travel 49 miles upstream, what is the speed of the boat in still water?"
Merci pour vos cogitations .
En ces temps de disette de problèmes,
aidez-moi à rédiger en Anglais la résolution de ce casse-tête:
"The current in a stream moves at a rate of 7 mph. If a boat travels 98 miles downstream in the same time that it takes to travel 49 miles upstream, what is the speed of the boat in still water?"
Merci pour vos cogitations .
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Verified answer
Hello,
We write v the speed of the boat in calm water and t the time of the travel.
We obtain the following system of equations:
t(v + 7) = 98
t(v - 7) = 49
So we have :
2 × t(v - 7) = 49 × 2
2t(v - 7) = 98
We can therefore establish the following equation:
2t(v - 7) = t(v + 7)
2tv - 14t = tv + 7t
2tv - tv = 7t + 14t
tv = 21t
v = 21t/t (if t ≠ 0)
v = 21
Thus, the speed is 21 mph