Question

Two planes start from a city and fly in opposite directions, one averaging a speed of 40 km/h greater than the others. If they are 3400km apart after 5h, the average speeds,respectively are
a. 330,370 km/h
b. 320,360 km/h
c. 250,290 km/h
d. 300,340 km/h

Answer 1

» (b) 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

Answer 2

average speed of one plane be x km/h

therefore average speed of other plane = (x+40)km/h.

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

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

according to the condition,

5x + 5 (x+40) = 3400

10x+200 = 3400

10x=3200

x=320

speed of 1st plane is 320km/hr

speed of 2nd plane is 320+40

                                      =360km/hr

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