百分數與變分

A box contains two kinds of coins: $\$5$ and $\$2$. The ratio of the number of $\$5$ coins to the number of $\$2$ coins is $4:5$. If the total value of the coins is $\$90$, then the total number of coins in the box is

The scale of a map is $1:20\,000$. If two buildings are $3.8\text{ cm}$ apart on the map, then the actual distance between the two buildings is

It is known that $y$ varies partly as $x$ and partly as $\sqrt{x}$. When $x=1$, $y=4$ and when $x=4$, $y=10$. Find $y$ when $x=16$.

John's daily working hours have increased from 8 hours to 10 hours but his hourly pay has decreased by $25\%$. Find the percentage change in John's daily income.

A sum of $\$8\,000$ is deposited at $1\%$ p.a., compounded yearly. Find the interest earned after 4 years. Give the answer correct to the nearest dollar.

Suppose $z$ varies directly as $x^2$ and inversely as $y$. When $x=4$ and $y=3$, $z=2$. When $x=2$ and $z=3$, $y=$

The scale of a map is $1:4\,000$. If the actual area of a sports field is $8\,000\text{ m}^2$, find its area on the map.

If $1$ Euro is equivalent to $6.94$ H.K. dollars and $1$ U.S. dollar is equivalent to $7.78$ H.K. dollars, how many Euros are equivalent to $100$ U.S. dollars? Give your answer correct to the nearest Euro.

The simple interest on a sum of money at $r\%$ p.a. for $4$ years is equal to the compound interest on the same amount at $4\%$ p.a. for $4$ years compounded half-yearly. The value of $r$, correct to 2 significant figures, is

If $2x=3y=4z$, then $\dfrac{x+y-z}{x-y+z}=$