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I need help with this word problem:
Flying in still air, an airplane travels 550 km/h. It can travel 1200 km with the wind in the same time that it travels 1000 km against the wind. Find the speed of the wind.
Thanks guys!
4 Answers
- Bob BLv 78 years agoFavorite Answer
The wind speed adds or subtracts from the airplane's speed. Since distance is rate times time, time is distance divided by rate:
Tu = 1000 / (550 - w) [upwind, wind speed subtracts]
Td = 1200 / (550 + w) [downwind, wind speed adds]
Since the times are the same, equate the two right sides:
1000 / (550 - w) = 1200 / (550 + w)
Cross-multiply:
1000(550 + w) = 1200(550 - w)
Divide both sides by 200 for convenience:
5(550 + w) = 6(550 - w)
Multiply out:
2750 + 5w = 3300 - 6w
Add 6w to both sides:
2750 + 11w = 3300
Subtract 2750 from both sides:
11w = 550
Divide both sides by 11:
w = 550 / 11 = 50
The wind is blowing at 50 km/h.
- PrakashLv 58 years ago
Speed against the wind in time t = 1000/t = 550 - wind speed, w
Speed along the wind in time t = 1200/t = 550 + wind speed, w
Dividing, we get 1000/1200 = (550 - w) / (550 + w)
or 10/12 = (550 - w) / (550 + w)
or 10*(550 + w) = 12*(550 - w)
or 5500 + 10w = 6600 - 12w
or 22w = 1100
or w, wind speed = 50 km/h