A train moves at 90 km/h to

Solution

ATQ, Let the usual time taken by the train be 'T' hours. Using, distance = speed × time We have, 'D' = 90T ----------- (I) And, 'D' = 100 × {T - (15/60)} -------- (II) From equation (I) and (II), We have, 90T = 100 × {T - (15/60)} Or, 90T = 100T - 100 × (15/60) Or, 10T = 25 Or, 'T' = 2.5 On putting the value of 'T' = 2.5 in equation (I), We have 'D' = 90 × 2.5 = 225 km So, the required time = (4 × 225) ÷ 120 = (900/120) = 7.5 hours