百分數與變分

A man sold a car for $\$35\,000$ at a loss of $30\%$ on the cost price. What would have been the loss or gain percent if he had sold it for $\$50\,500$?

If the length of a rectangle is increased by $10\%$ and the width decreased by $10\%$, which of the following is true?

A certain sum of money is just sufficient to pay the wages of one man for $m$ days or the wages of one boy for $n$ days. For how many days will this sum be just sufficient to pay the wages of one man and one boy together?

$\$P$ amounts to $\$Q$ in $n$ years at simple interest. The rate per annum is