Abhishek makes a profit of $Rs.\,110,$ if he sells a certain number of pens he has at the price of $Rs.\, 2.5$ per pen and incurs a loss of $Rs.$ $55,$ if he sells the same number of pens for $Rs.$ $1.75$ per pen. How many pens does Abhishek have?

A manufacturer fixes his selling price at $33 \%$ over the cost of production. If cost of production goes up by $12 \%$ and manufacturer raises his selling price by $10 \%,$ his percentage profit is

A man sells two article for $Rs.\,5000$ each neither losing nor gaining in the deal. If he sold one of them at a gain of $25 \%,$ the other article is sold at a loss of.......$\%$

If the discount of $10 \%$ is given on the marked price of a radio, the gain is $20 \%$. If the discount is increased to $20 \%,$ the gain is......$\%$

Present age of Bob is equal to Abby's age $8\, years$ ago. Four years hence, the respective ratio between Bob's age and Abby's age will be $4: 5$ at that time. What is Bob's present age? (in $years$)

Articles are marked at a price which gives a profit of $25 \%$. After allowing a certain discount the profit reduces to $12\frac{1}{2} \%$. The discount percent is