百分數與變分

A man drives 20 km at 40 km/h. At what speed must he drive on his return journey so that the average speed for the double journey is 60 km/h?

The marked price of a book is $\$240$. If the book is sold at a discount of 20%, the profit will be 20% of the cost price. What is the cost price of the book?

Coffee $A$ and coffee $B$ are mixed in the ratio $1:2$. A profit of 20% on the cost price is made by selling the mixture at $\$36$/kg. If the cost price of $A$ is $\$12$/kg, what is the cost price of $B$?

The marked price of a book is $\$x$. $30\%$ of this price is profit. If the book is sold at a discount of $20\%$, what will the profit then be?

A group consists of $n$ boys and $n$ girls. If two of the girls are exceeded by two other boys, then $51\%$ of the group members will be boys. What is $n$?

A merchant sold $100$ chairs. $80$ of them were sold at a profit of $30\%$ on each chair, while $20$ of them were sold at a loss of $40\%$ on each chair. What is his percentage gain or loss on the whole stock?

The running speeds of three boys $A$, $B$ and $C$ are in the ratios $a:b:c$. The times that $A$, $B$ and $C$ take to complete a $1500\text{ m}$ race are in the ratios

A factory employs $x$ workers each working $n$ hours a day. The whole factory produces $k$ watches per day. If $y$ workers go on leave, then how many hours a day should the remaining workers work in order to produce the same number of watches per day?

The daily wages of a man and a boy are in the ratio $2:1$. In a day a man has to work $8$ hours but a boy only $6$ hours. The hourly wages of a man and a boy are in the ratio

When the hour hand has turned through an angle $x^\circ$, what is the angle through which the minute hand has turned?