Question

IF THE C.P OF 8 PENS IS SAME AS S.P OF 10 PENS. HOW TO CALCULATE THE PROFIT OR LOSS PERCENT MADE,IF ALL PENS BOUGHT ARE TO BE SOLD

Answer 1

Cost of 8 pen let x, So the cost of per pen is x/8
and sale price of 10 pen is x and cost of per pen is x/10

so the profit : {(x/8 - x/10)/x/8} * 100 = you will get the percentage of profit. 

Answer 2

Let the C.P of each pen be Re 1
C.P of 10 pens is = Rs 10
S.P of 10 pens is = C.P of 8 pens = Rs 8
Since, C.P>S.P,
Therefore, Loss = C.P - S.P
                       = Rs 10 - Rs 8 = Rs 2
Hence, Loss% = (Loss/C.P) x 100
                      = (2/10) x 100
                      = 20%