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A shopkeeper buys a certain number of pens. If the selling price of 5 pens is equal to the cost price of 7

pens, find his profit or loss percentage Looking to do well in your science exam ? Learn from an expert tutor. Book a free class!

Consider ₹ x as the C.P. of 7 pens

C.P. of 1 pen = ₹ x/7

Based on the question

S.P. of 5 pens = ₹ x

S.P. of 1 pen = ₹ x/5

Profit = S.P. – C.P.

Substituting the values

= x/7 – x/5

Taking LCM

= (7x – 5x)/ 35

= ₹ 2x/ 35

We know that

Profit % = Profit/C.P. × 100 %

Substituting the values

= 2x/ 35/ x/7 × 100 %

It can be written as

= 2x/35 × 7/x × 100 %

By further calculation

= 2/5 × 100 %

So we get

= 2 × 20 %

= 40 %

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