3 friends went to buy a clock valued in $ 60 and they contributed $20 each for the clock. Later the shopkeeper discovered that it was of $ 50 only and sent a servant to return them $ 10. The servant unable to divide 10 among the 3, keeps $4 for himself and gives them 2$ each. So now each friends expenditure is $ 18 only 18*3=54 so $ 54 given by the friends and 4 $ are with the servant total = 54+4 = 58.
Where did 2$ go?
Our mind is thinking just of what each got
rather we should see where the amount goes 18*3=54 is what they spent and 6 is what they were reimbursed so total = 60 money given to the servant gets automatically accounted for, as the shares of friends gets reduced.