If the cost price of 15pens is equal to the selling price of 20pens ,then the loss percent is

@ shishanth 
i can help u by providing a way to do this ques , rest u have to do calculation and find out 
let the cost price of of each pen to be x 
cost price of 20 pens = rs 20 
selling price of 20 pens = cost price of 15 pens = rs  15 
now loss = CP – SP = 20 – 15 = 5
after calculating that u need to apply the following formula 
loss percent = loss / cp  * 100
and then calculate the valuie 
HOPE IT CLEARS