百分數與變分

$X$ sells an article to $Y$ at a profit. $Y$ then sells it to $Z$ for $\$60$ at a profit of $20\%$. If $X$ had sold the article directly to $Z$ for $\$60$, how much MORE profit would he have made?

A car travels from $P$ to $Q$. If its speed is increased by $k\%$, then the time it takes to travel the same distance is reduced by

A bag contains $n$ balls of which $60\%$ are red and $40\%$ are white. After 10 red balls are taken out from the bag, the percentage of red balls becomes $50\%$. Find $n$.

The weight of a gold coin of a given thickness varies as the square of its diameter. If the weights of two such coins are in the ratio $1:4$, then their diameters are in ratio

The radii of two solid spheres made of the same material are in the ratio $2:3$. If the smaller sphere weighs 16 kg, then the larger one weighs

Find, correct to the nearest dollar, the compound interest on $\$10\,000$ at $8\%$ p.a. for 4 years, compounded half-yearly.

If the selling price of 5 pens is the same as the cost price of 6 pens, the percentage profit in selling a pen will be

If $a:b=3:2$, $b:c=4:3$, then $a+b:b+c=$

Peter bought an article for $\$x$. He sold it to Mary at a profit of $20\%$. Mary then sold it to John for $\$90$ at a loss of $25\%$. Find $x$.

If $a$ is $10\%$ less than $b$ and $b$ is $10\%$ greater than $c$, then $a:c=$