FORTNIGHT'S PUZZLE 5

PUZZLE 5: 30th November-6th December (to be e-mailed by the 7th December)
POSTED BY IES CAMPANAR

THE AIRCRAFT
A light aircraft has just flown 400 kilometres. The aircraft covered the first 100 kms at a speed of 150 kph, the next 100 at 300 kph, the following 100 at 450 kph, and the last 100 at 600 kph.Can you figure out the average speed of the aircraft on its 400 kilometres journey?

SOLUTION
t = e/v (t = time, e = space, v = velocity)t1 = 100/150 = 2/3t2 = 100/300 = 1/3t3 = 100/450 = 2/9t4 = 100/600 = 1/6T = 2/3 + 1/3 + 2/9 + 1/6 = 25/18v = E/ T = 400 : (25/18) = 288 kph