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

Ram purchased a computer set for $Rs. 12500$ and spent $Rs. 300$ on transportation and $Rs. 800$ on installation. At what price should he sell it to earn an overall profit of $15\%$? (in $Rs.$)

If a radio is purchased for $Rs. 490$ and sold for $Rs. 465.50$,find the $\text{loss} \%$. (in $\%$)

$A$ shopkeeper purchased $70$ $kg$ of potatoes for $Rs. 420$ and sold the whole lot at the rate of $Rs. 6.5$ per $kg$. What will be his gain percent?

$A$ loss of $19 \%$ gets converted into a profit of $17 \%$ when the selling price is increased by $Rs. 162$. Find the cost price of the article in $Rs.$

$A$ shopkeeper purchased $245$ pieces of an article at $Rs. 30$ per piece. He spent $Rs. 980$ on transport and $Rs. 1470$ on packing the articles. He sold the articles at the rate of $Rs. 50$ per piece. What is the percent profit earned?