Walking at 3/5 of his usual speed, a man is 4 hours too late. Find his usual time.

Suppose the usual speed of the man be x km/hr .

Let distance travelled be D km

Therefore usual Time taken = D / x

.’. walking speed = 3/5. x

Let distance travelled be D km

we can write

D/(3/5 . x)- D/x = 4

Or D((5 / 3. x) – 1/x) = 4

Or D/x ((5 / 3 ) – 1) = 4

Or D/x (2 / 3) = 4

But D/x = Usual Time taken by the man .

T= 12/2

or T= 6 hours . __Answer __