If $5 \%$ more is gained by selling an article for $Rs. 350$ than by selling it for $Rs. 340$,the cost price of the article is:

$A$ man sells each of his $2$ articles for $Rs. 99$. On one he gains $10 \%$ and on the other he incurs a loss of $1 \%$. What is his total gain in $\%$ in the entire transaction?

The marked price of a bed is $Rs. 2400$. The shopkeeper gives successive discounts of $10 \%$ and $X \%$ to the customer. If the customer pays $Rs. 1836$ for the bed,then find the value of $X$ in $\%$.

$A$ man sold his two cars for $Rs. 4.5$ lakh each. In the sale of the first car, he incurred $20\%$ profit, and in the sale of the second, he incurred $20\%$ loss. What is the total amount of profit or loss?

When a book is sold at its Marked Price,it gives a profit of $40 \%$. What percentage of profit or loss will occur if it is sold at half the Marked Price?

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)?