A man is riding a bike with front and back wheel circumference of 40 inches and 70 inches respectively. If the man rides the bike on a straight road without slippage, how many inches will the man have travelled when the front wheel has made 15 revolutions more than the back wheel?

Given the ratio of the circumference of front wheel  is 40 inches and back wheel is 70 inches. 

Distance covered = Circumference of the wheel × No. of Revolutions made by the wheel

If n is the number of revolutions made by back wheel, the number of revolutions made by front wheel is n+15

Distance covered by both the wheels is the same

i.e, 40*(n+15)=70n

 n=20 

                Front wheel      :      Back Wheel 

 Circumference       40      :      70 

 Revolutions           35      :      20

Distance covered  :  40×35 = 70×20 = 1400 inches.