When there are two successive profits of $$x\%$$ and $$y\%$$ then the net percentage profit $$=\ \dfrac{\ x+y+xy}{100}$$.
When there is a profit of $$x\%$$ and loss of $$y\%$$ then net percentage profit or loss $$=\ \dfrac{\ x-y-xy}{100}$$
If the original price of a product is P and an increase of x% is made, the resultant price of the product will be $$P(1+\frac{x}{100})$$
Similarly, if the original price of a product is P and a decrease of x% is made, the resultant price of the product will be $$P(1-\frac{x}{100})$$
