A man covers a certain distance on bike. Had he moved 4 kmph faster, he would have taken 72 minutes less. If he moves slow by 4 kmph, he will take hours more to cover the distance. What is the distance travelled by him ? Choose the correct answer
A) 48 km
B) 56 km
C) 64 km
D) 96 km
E) 106 km
Explanation :   Let the distance be 'D' and the speed be 'x' kmph.   96 km/x + 4 = 96 km/x - 72/60   96 km/x - 96 km/(x - y) = 6/5 = 96 km(x + 4 - x)/x(x - 4) = 6/5   ∴ 96 km/x(x + 4) = 3/10 ......(i)   96 km/x - 4 - 96 km/x = 2   ∴ 96 kmx - 96 kmx + 496 km/x(x - 4) = 2   ∴ 96 km/x(x - 4) = 1/2 .....(ii)   From equation (i) and (ii):   3/10 x (x + 4) = 1/2 x(x - 4)   ∴ 3(x + 4) = 5(x - 4) = 3x + 12 = 5x - 20   2x = 32 ∴ x = 16 kmn-1   ∴ 96 km = x(x - 4)/2 = 16x12/2 = 16x6 = 96 km   Answer : Option 96 km
<result>D</result>
A man covers a certain distance on bike. Had he moved 4 kmph faster, he would have taken 72 minutes less. If he moves slow by 4 kmph, he will take hours more to cover the distance. What is the distance travelled by him ?