Theory:

1. If the cost price is lesser than the selling price, then there is a profit.
 
\(\text{Profit}\) \(=\) \(\text{S.P.}\) \(-\) \(\text{C.P.}\)
 
2. If the selling price is lesser than the cost price, then there is a loss.
 
\(\text{Loss}\) \(=\) \(\text{C.P.}\) \(-\) \(\text{S.P.}\)
 
3. If the cost price equals the selling price, then there is neither profit nor loss.
 
\(\text{C.P.}\) \(=\) \(\text{S.P.}\) (Neither profit nor loss)
 
4. \(\text{Discount}\) \(=\) \(\text{M.P.}\) \(-\) \(\text{S.P.}\) (or) \(\text{S.P.}\) \(=\) \(\text{M.P.}\) \(-\) \(\text{Discount}\)
 
5. If there is no discount, then \(\text{M.P.}\) \(=\) \(\text{S.P.}\)
Example:
1. If C.P. \(= Rs.1200\), S.P. \(= Rs.1500\), find profit or loss.
 
In this case, S.P. \(>\) C.P.
 
\(\text{Profit}\) \(=\) \(\text{S.P.}\) \(-\) \(\text{C.P.}\)
 
\(=\) \(1500\) \(-\) \(1200\) \(= Rs.300\)
 
Profit \(= Rs.300\)
 
 
2. If C.P. \(= Rs.2000\), S.P. \(= Rs.1000\), find profit or loss.
 
In this case, C.P. \(>\) S.P.
 
\(\text{Loss}\) \(=\) \(\text{C.P.}\) \(-\) \(\text{S.P.}\)
 
\(2000 - 1000\) \(=\) \(Rs.\)\(1000\)
 
Loss \(=\) \(Rs.\)\(1000\)
 
  
3. If C.P. \(= Rs.2200\), S.P. \(= Rs.2200\), find profit or loss.
 
In this case, \(\text{C.P.}\) \(=\) \(\text{S.P.}\)
 
Therefore, there is neither profit nor loss.
 
  
4. If the M.P. \(= Rs.10000\), S.P. \(= Rs.9000\), find discount.
 
\(\text{Discount}\) \(=\) \(\text{M.P.}\) \(-\) \(\text{S.P.}\)
 
\(= 10000 - 9000\)
 
\(= Rs.1000\)
 
  
5. If M.P. \(=\) \(Rs.1550\), Discount \(= Rs.250\), find S.P.
 
\(\text{S.P.}\) \(=\) \(\text{M.P.}\) \(-\) \(\text{Discount}\)
 
\(= 1550 - 250\)
 
\(= Rs.1300\)
 
  
6. If M.P. \(= Rs.200\), S.P. \(= Rs.200\), find discount.
 
In this case, \(\text{M.P.}\) \(=\) \(\text{S.P.}\)
 
So, there is no discount.