Percentage：練習題

A student scored \( 18 \) out of \( 25 \) in a mathematics test. What is the score expressed as a percentage?

A rectangular field has its length and width increased by \( 20\% \) and \( 10\% \) respectively. Calculate the percentage increase in the area of the field.

A sum of money was invested in a bank at a compound interest rate of \( r\% \) per annum, compounded yearly. If the principal amount doubled after 10 years, which of the following expressions represents \( r \)?

The price of a laptop after a \( 15\% \) discount is \( \$1,020 \). Calculate the original price of the laptop before the discount.

Express \( 45 \) minutes as a percentage of \( 2.5 \) hours.

A company's annual profit increased by 15% in 2022 to reach \$460,000. In 2023, the profit then decreased by 10% from the 2022 level. Calculate the total profit the company made in the year 2021.

A rectangular plot of land has its length increased by \( 25\% \) and its width decreased by \( 20\% \). Calculate the percentage change in the total area of the land.