Question 325959
with the wind plane travels 540 mi in 2 hr. 
flying against , the plane travels 690 mi in 3 hr. 
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let speed of plane in still air be x mph
& speed of wind be y mph
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With wind
Time taken = 540 / x+y= 2
540 =2x+2y
270=x+y........................1
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Against wind 
Time taken = 690/ x-y = 3
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690=3x-3y
230=x-y........................2
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Add equation 1 & 2
x+y+x-y=270+230
2x=500
x=250 mph speed of plane
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plug the value of x in equation 1
270=250+y
y= 20 mph the speed of wind