百分數與變分

If $3a=2b=5c$, then $\dfrac{1}{a}:\dfrac{1}{b}:\dfrac{1}{c}=$

A man walks from place $A$ to place $B$ at a speed of $3\text{ km/h}$ and cycles immediately back to place $A$ along the same road at a speed of $15\text{ km/h}$. The average speed for the whole trip is

A man drives a car at $45\text{ km/h}$ for $3$ hours and then at $50\text{ km/h}$ for $2$ hours. His average speed for the whole journey is

If the compound interest on $\$1000$ for two years at $9\%$ p.a., paid half-yearly is $\$x$, find $x$.

The marked price of an article is originally $P$. The marked price is then increased so that when a discount of $10\%$ is made on the new marked price, the selling price is still $P$. What is the new marked price?

Ten litres of a mixture contain $60\%$ of alcohol and $40\%$ of water by volume. How many litres of water should be added so that it contains $30\%$ of alcohol by volume?

If $A$, $B$ and $C$ can finish running the same distance in $3$, $4$ and $5$ minutes respectively, then $A$'s speed : $B$'s speed : $C$'s speed $=$

If $a:b=1:2$ and $b:c=1:3$, then $a+b:b+c=$

A hawker bought 120 apples and the cost was $\$90$. It was found that $\dfrac{1}{8}$ of the apples were rotten and could not be sold. He sold the rest at $\$1$ each. What percentage of the cost was his profit?

The marked price of a book is double that of its cost. In a sale, what percentage discount was given if the profit made was $20\%$ of the cost?