Percentages

The longer side is the known side plus its percentage increase: other side = a × (1 + p/100). Then multiply the two side lengths: S = a × other side. Express the area in cm².

p% of n = n × p ÷ 100. Useful shortcuts: 10% is one tenth, 20% one fifth, 25% one quarter and 50% one half.

Divide the part by the whole and multiply by 100: percentage = d ÷ n × 100. For example, 15 out of 60 is 15 ÷ 60 × 100 = 25%.

Interest is calculated from the current balance each year, so in the second year it is also earned on the first year’s interest.

1. Convert the annual percentage into a multiplier: 1 + percentage ÷ 100.
2. Multiply the initial deposit by this multiplier once for the first year.
3. Multiply the new balance by the same multiplier again for the second year.

Formula: final amount = initial deposit × (1 + annual percentage ÷ 100)².

First find the discount amount: original price × percentage ÷ 100. Subtract it from the original price. New price = original price × (1 − p/100).

The discount is the part of the original price that must be subtracted.

1. Divide the discount percentage by 100.
2. Multiply the result by the original price to find the discount amount.
3. Subtract the discount amount from the original price.

Formula: discounted price = original price × (1 − discount ÷ 100).

Find the discounted unit price, multiply by the quantity and subtract the total cost from the money available.

For store A, add delivery to the price after the percentage discount. For B, subtract the stated euro discount. Compare the total prices.

Find the second-year harvest by multiplying the first-year amount by (1 + b/100). The third-year increase is based on the second-year harvest, so multiply that amount by (1 + c/100). Finally add the harvests for all three years.

Find the price difference. Divide by the original price and multiply by 100; do not divide by the new price.