Two planes start from a city and fly in opposite directions, one averaging a speed of 40 kmph greater than the second. If they are 3400 km apart from each other in 5 hours, the sum of their average speeds, is

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Solution

Let average speed of one plane be x km/h

Then, average speed of other plane be (x+40)km/h.

Distance travelled by first plane in 5h = 5x km

Distance travelled by second plane in 5h
= 5 (x+40)km

5x + 5 (x+40) = 3400
10x+200 = 3400 → 10x = 3200

.°. x = 3200/10 = 320km/h

So, average speed of second plane
= 320+40 = 360km/h

Therefore Sum of their avg speeds = 320 + 360 = 680 km/h

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