Percentages：练习题

A piece of industrial machinery was valued at \(\pounds 12,000\) at the start of 2021.
The value of the machinery depreciates by \(15\%\) each year.
Work out the value of the machinery at the start of 2023.

The length of a rectangle is increased by \(20\%\) and its width is decreased by \(20\%\).
Work out the overall percentage change in the area of the rectangle.

Olivia invests \(\pounds 5000\) for 3 years in a savings account that pays \(2\%\) compound interest per annum.
Calculate the total interest she will have earned at the end of the 3 years.

The population of a town increased by \(10\%\) in 2021 and then decreased by \(5\%\) in 2022.
At the end of 2022, the population was 20,900.
What was the population at the start of 2021?

Calculate \(12\%\) of \(350\).

A technology store increases the price of a television by \(20\%\). During a sale, they then decrease this new price by \(10\%\). If the sale price is \(\pounds 432\), work out the original price of the television using percentages.

An item is priced at \(\pounds 120\). Calculate the new price after a percentage increase of \(15\%\).

A coat is sold in a sale for \( \pounds 153 \).
This sale price is a result of a 15% discount on the original price.

Calculate the original price of the coat.

Emma invests \(\pounds 4500\) in a savings account for 3 years. The account pays compound interest at a rate of \(2.5\%\) per year.

(a) Calculate the total amount of money in the account at the end of 3 years.

(b) After 3 years, the value of a car she owns has depreciated by \(12\%\) from its value of \(\pounds 8000\). Calculate the new value of the car.