Terminology 

Cost Price 

It is the expenditure in curred on the purchase or the production of the article which can be taken as investment on the article

Selling Price

It is the revenue generated by selling the particular article

Profit or Loss

The difference of selling price and cost price is called profit value or loss 

selling price is greater than cost price  then it is profit if cost price is greater than selling price then it is loss

Marked Price 

It is the price of the product being displayed on the label it is taking generally as list price or MRP

Discount

it is the rebate given to the customer before selling of the article

Formulae

Profit =SP-CP

Loss = CP - SP

when there is profit%

SP =( 100+profit%/100) ×CP 

when there is loss%

SP = (100- loss% /100)×CP

If cost price of m articles is equal to selling price of n articles 

Net% = (m-n/n) ×100

if m>n gain

if m<n loss