Question

A man purchased 4mangoes at the rate of 5 rupees and sold 5mangoes at the rate of 4rs. .find loss percentage?

Answer 1

cost price of 4 mangoes =5 rupees
selling price of 5 mangoes=4 rupees 
loss= cost price - selling price
      = 5 rupees - 4 rupees
      = 1 rupees
loss percent = 1/5*100 =20%

Answer 2

Always compare Selling price and Cost price for the same Quantity of the particular item ( here mangoes is the item ) .

Generally, in the answers to such questions people compare CP and SP for 1 item but you can compare for any fixed amount ( 100 , 200 , 541 , 98 , etc. ) let's say for x amount.

CP of 4 mangoes = rs. 5

CP of x mangoes = rs. (5/4)*x

SP of 5 mangoes = rs. 4

SP of x mangoes = rs. (4/5)*x

Now (5/4)*x>(4/5)*x

( x being a positive whole number )

Hence there occurs a loss as CP > SP ( for x mangoes ) .

Loss = [(5/4)-(4/5)]*x = (9/20)*x

So loss % = (loss/CP) * 100

= (9/20)*(4/5)*100 = 36