百分數與變分

By selling an article at $10\%$ discount off the marked price, a shop still makes $20\%$ profit. If the cost price of the article is $\$19\,800$, then the marked price is

Coffee $A$ and coffee $B$ are mixed in the ratio $x:y$ by weight. $A$ costs $\$50$/kg and $B$ costs $\$40$/kg. If the cost of $A$ is increased by $10\%$ while that of $B$ is decreased by $15\%$, the cost of the mixture per kg remains unchanged. Find $x:y$.

Let $y$ vary partly as $\dfrac{1}{x}$ and partly as $x$. When $x=1$, $y=5$ and when $x=4$, $y=\dfrac{25}{2}$. Find $y$ when $x=2$.

If $\dfrac{1}{a}:\dfrac{1}{b}=2:3$ and $a:c=4:1$, then $a:b:c=$

A blanket loses $10\%$ of its length and $8\%$ of its width after washing. The percentage loss in area is

A man borrows $\$10\ 000$ from a bank at $12\%$ per annum compounded monthly. He repays the bank $\$2000$ at the end of each month. How much does he still owe the bank just after the second repayment?

$3\text{ kg}$ of a solution contains $40\%$ of alcohol by weight. How much alcohol should be added to obtain a solution containing $50\%$ of alcohol by weight?

$P$ sold an article to $Q$ at a profit of $25\%$. $Q$ sold it to $R$ also at a profit of $25\%$. If $Q$ gained $\$500$, how much did $P$ gain?

If $a:b=3:4$ and $b:c=2:5$, then $a^2:c^2=$

If 1 U.S. dollar is equivalent to 7.8 H.K. dollars and 1000 Japanese yen are equivalent to 53.3 H.K. dollars, how many Japanese yen are equivalent to 50 U.S. dollars?