If on selling $12$ notebooks,a seller makes a profit equal to the selling price of $4$ notebooks,what is his percent profit?

$A$ person earns $15 \%$ on an investment but loses $10 \%$ on another investment. If the ratio of the two investments is $3:5$,what is the gain or loss percentage on the two investments taken together (in $\%$)?

If the cost price of $20$ tables is equal to the selling price of $25$ tables,find the loss percentage. (in $\%$)

Sarita sells a phone at a profit of $20 \%$. If she had bought it at $20 \%$ less and sold it for $Rs. 180$ less, she would have gained $25 \%$. Find the cost price of the phone in $Rs.$

$A$ fan in a shop is offered at a discount of $10 \%$. It is sold during a clearance sale at an additional $6 \%$ discount over the already discounted price for $Rs. 846$. The original marked price of the fan is (in $Rs.$)

$A$ person sells a colour $TV$ at $10\%$ below the cost price. Had he received $Rs. 1494$ more,he would have made a profit of $12 \frac{1}{2}\%$. What was the cost price of the colour $TV$ (in $Rs.$)?