Question

the cost price of 11 pens is equal to the selling price of 10 pens find the loss or gain percent

Answer 1

Cp in this case = rupees 10 ( Sp of 10 pens = cp of 11pens)
Therefore
Sp = 11
Profit = 1 (11-10)
Profit℅= 1/10*100
= 10℅

Answer 2

Let the CP of 1 pen be a

CP of 11 pen = 11a

SP of 10 pen = CP of 11 pen = 11a

SP of 1 pen = 11a/10

Gain = SP - CP

= 11a/10 - a

= a/10


Gain % = Gain *100/CP

= (a/100)*100/a

= 100/10

= 10%