A retailer buys 40 pens at a marked price of 36 pens from a wholesaler. If he sells these pens giving a discount of 1%, what is his profit percent?

Given, •CP of 40pens = Marked Price of 36 pens
•Sells these 40pens at 1% discount.
Find the profit%?
profit% on 40pens would be:
{ (SP of 40pens - CP of 40pens) / CP of 40 pens } x 100 -----------> equation 1

Thus,
We need to find •CP of 40 pens.
• SP of 40 pens.

For CP of 40 pens:
Since CP of 40pens = MP of 36 pens
let, MP of 1 pen = 1Rs
then,CP of 40 pens = Marked price of 36 pens = 36Rs. (Since CP, MP Relation is given in ques)

Now for SP of 40 pens

we know the retailer sells these 40pens at a discount of 1%, and the discount is always given at the marked price.
And 1% discount on marked price means the item will be sold at 99% of the marked price

Marked price of 40 pen would be 40Rs( one pen MP is 1rs)
So SP(Selling price) of 40 pens would be 99% of Marked price of 40 pens
The SP of 40 pens = (99 /100) x 40Rs
= 39.6 Rs
Profit% of 40 pens -------- using equation 1
= {(39.6-36)/36} x 100
= 10%

Customer ne 36 pen purchase kiye to cp of retailer
36 pen ka cp =36 /-
Then sell 40 pen at 1% discount so s.p= 40*99/100
S.p = 39.6 /-
Profit= sp-cp
= 39.6-36
3.6 /-

Profit%= (3.6/36)*100= 10%

bought 40 pen at MP of 36 pen
let for 1 pen ,MP =100
hence for 40 pen(i.e 40*1=40) ,MP=3600 (i.e 36*100=3600)
hence
CP/pen=3600/40=90

SP/pen=100-1%=99

profit=9(i.e 99-90=9)
hence % profit=9/90*100=10%

Good Explanation @Sudhakar.

Let the marked price of each pen be 1 Rs.
Then he buys 40 pens at 36 Rs. (Since 40 pens at the marked price of 36 pens)
So, the price of each pen = 36/40 = 0.9 Rs.
While selling he makes 1% discount from the marked price 1 Rs. Thus, he sells at 0.99 Rs.
Profit for a pen = 0.99 - 0.9 = 0.09
In percentage, profit = (0.09 / 0.9) x 100 = 10%
Answer = 10%