百分數與變分

John spends 40 minutes to walk from his home to school. If he increases his walking speed by $2\text{ km/h}$, then it takes only 30 minutes. What is the distance between John\'s home and his school?

$60\%$ of the students in a school are boys. $70\%$ of the boys and $40\%$ of the girls wear glasses. If 696 students wear glasses, how many students are there in the school?

A number is first reduced by $p\%$ and then increased by $x\%$. If the number so obtained is the same as the original number then $x=$

The length and width of a cuboid are each increased by $10\%$ and the height remains unchanged. The percentage increase in volume is

$\$10\,000$ is invested for 2 years at $10\%$ per annum, compounded half-yearly. The compound interest, correct to the nearest dollar, is

$A$ is $25\%$ taller than $B$. $B$ is $25\%$ shorter than $C$. $A$'s height : $C$'s height $=$

A man drives a car at 30 km/h for 3 hours and then at 40 km/h for 2 hours. His average speed for the whole journey is

$A$ alone can complete a job in 8 hours. $B$ alone takes 12 hours and $C$ alone takes 6 hours. After $A$ and $B$ have worked together on the job for 3 hours, $C$ joins them. How much longer will they take to complete the job?

The marked price of a book is $20\%$ above the cost price. If the book is sold at a discount of $10\%$ off the marked price, what is the gain per cent based on the cost price?

Last year, a man saved $10\%$ of his income. By how much per cent must his income be increased if his expenditure increased by $20\%$ and he wants to save $20\%$ of his income?