1. Gain percent = (Gain × 100)/(C.P.)

    Loss percent =  (Loss × 100)/(C.P.)

2. When the selling price and gain percent are given:

    C.P.= (100/(100+Gain%))×S.P.

3. When the cost and gain percent are given:

    S.P=((100+Gain%)/100)×C.P.

4. When the cost and loss percent are given:

    S.P.=((100-Loss%)/100)×C.P

5. When the selling price and loss percent are given.

    C.P=(100/(100-Loss%))×S.P

6. If a man buys x items for Rs. y and sells z items for Rs. w, then the gain or loss percent made by him is
    (xw/zy-1)×100%

7. If the cost price of m articles is equal to the selling price of n articles, then % gain or loss

    ((m-n)/n)*100

    [if m>n, it is % gain and if m,n, it is % loss]

    (S.P1)/(100+x)=(S.P2)/(100+y)=(C.P.)/100=(S.P_1-S.P_2)/(x-y)

     Where x or y is -ve, if it indicates a loss, otherwise it is +ve

9. If ‘A’ sells an article to ‘B’ at a gain/loss of m% and ‘B’ sells it to ‘C’ at a gain/loss of n% If ‘C’ pays Rs. z for it to ‘B’ then the cost price for ‘A’ is

     where m or n is –ve, it indicates a loss, otherwise, it is +ve.

10. If ‘A’ sells an article to ‘B’ at a gain/loss of m% and ‘B’ sells it to ‘C’ at a gain/loss of n%, then the resultant profit/loss percent is given by

      (m+n+mn/100)

      where m or n is -ve, if it indicates a loss, otherwise it is +ve

11. When two different articles are sold at the same selling price, getting gain/loss of x% on the first and gain/loss of y% on the second, then the overall% gain or % loss in the transaction is given b     

       The above expression represents overall gain or loss accordingly as its sign is +ve or -ve

12. When two different articles are sold at the same selling price getting a gain of x% on the first and loss of x% on the second, then the overall% loss in the transaction is given by

      (x/10)²% ( Note that in such questions there is always a loss)

13. A merchant uses faulty measure and sells his goods at gain/loss of x%. The overall % gain/loss(g) is given by

      (100+g)/(100+x) = (True measure)/(Faulty measure)

      Note:- If the merchant sell his goods at cost price , then x = 0

14. A merchant uses y% less weight/length and sells his goods at gain/loss of x%. The overall % gain/loss is given by

      [{(y+x)/(100-y)}*100]%

15. A person buys two items for Rs. A and sells one at a loss of l% and other at a gain of g%. If each item was sold at the same price, then
      The cost price of the item sold at gain

       A(100-%loss)/(100-%loss)+(100+gain)

16. If two successive discounts on an article are m% and n%, respectively, then a single discount equivalent to the two successive discounts will be

      (m+n-mn/100)%