CAYLUS
Answered

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 .

Sagot :

SKABETIX

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