Question 1

How do I calculate a percentage of a number?

Accepted Answer

To find X% of Y, multiply Y by X and divide by 100. For example, 20% of 150 = (20 ÷ 100) × 150 = 30.

Question 2

How do I calculate percentage change?

Accepted Answer

Percentage change = ((New Value − Old Value) ÷ Old Value) × 100. For example, a change from 80 to 100 = ((100 − 80) ÷ 80) × 100 = 25% increase.

Question 3

How do I find what percentage one number is of another?

Accepted Answer

Divide the first number by the second, then multiply by 100. For example, 30 is what percent of 150? (30 ÷ 150) × 100 = 20%.

Question 4

How do I increase or decrease a number by a percentage?

Accepted Answer

To increase a number by X%: multiply by (1 + X/100). To decrease by X%: multiply by (1 − X/100). For example, 200 increased by 15% = 200 × 1.15 = 230.

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