Question

if selling price of 5 pens is equal to the cost price of 4 then the gain or loss percentage is what?

Answer 1

sp of 5 pen = cp of 4 pen
let cp of 4 pen = Rs 4
cp of 5 pen = Rs 5
sp of 5 pen = Rs 4
loss = Rs 1
loss % = 1*100/5 = 20%

Answer 2

Define x:

Let the cost of 1 pen = x

Find the selling price of 1 pen:

5 pens = 4x

1 pen = 4/5 x

Find the profit / loss:

Cost Price > Selling Price => it is a loss

Loss = Cost Price - Selling Price

Loss = x - 4/5 x = 1/5 x

Find the loss percentage:

Loss Percentage = 1/5 x 100 = 20%

Answer: The loss is 20%