百分數與變分

The cost price of a toy is $\$100$ and the marked price is $\$140$. If the toy is sold at $10\%$ discount of the marked price, the profit is

It is given that $y$ varies inversely as $x$. If $x$ is increased by $50\%$, then $y$ is decreased by

A bank offers loans at an interest rate of $18\%$ per annum, compounded monthly. A man took a loan of $\$20\,000$ and repays the bank in monthly instalments of $\$4\,000$. Find the outstanding balance after his first instalment.

$40\%$ of the students in a class failed in a test. They had to sit for another test in which $70\%$ of them failed again. Find the percentage of students who failed in both tests.

If $\dfrac{x+3y}{2x-y}=\dfrac{2}{3}$, then $\dfrac{x-y}{x+y}=$

Suppose $y$ is partly constant and partly varies inversely as $x$. When $x=1$, $y=7$ and when $x=3$, $y=3$. Find $y$ when $x=2$.

A man bought two books at $\$30$ and $\$70$ respectively. He sold the first one at a profit of $20\%$ and the second one at a loss of $10\%$. On the whole, he

$y$ varies directly as $x^2$ and inversely as $\sqrt{z}$. If $y=1$ when $x=2$ and $z=9$, find $y$ when $x=1$ and $z=4$.

Tea $A$ and tea $B$ are mixed in the ratio $x:y$ by weight. $A$ costs $\$80$/kg and $B$ costs $\$100$/kg. If the cost of $A$ is increased by $10\%$ and that of $B$ is decreased by $12\%$, the cost of the mixture per kg remains unchanged. Find $x:y$.

In a class, students study either History or Geography, but not both. If the number of students studying Geography is $50\%$ more than those studying History, what is the percentage of students studying History?