Question
A TOY CAR TRAVELS FROM A TO B AT A CONST. SPEED OF 20 km/h & IMMEDIATELY RETURNS TO A AT A CONST. SPEED v. IF THE AVG. SPEED OF THE CAR IS 24 km/h . THEN v IS = ?
Joshi sir comment
total distance = d+d = 2d km.
total time taken = d/20 + d/v hours
so avg. speed = 2d/[d/20 + d/v]
or 24 = 2/[1/20 + 1/v]
or 12 = 1/[1/20 + 1/v]
or 1/20 + 1/v = 1/12
or 1/v = 1/12 - 1/20
or 1/v = 2/60
or v = 30