What is X percent of a number?

Percent means "per 100", so if we're asking what is 25% of 16, we view it as 25 of 100 (or 25 divided by 100) which equals 0.25 in decimal form. We can then multiple that decimal by 16 to get our answer. So 0.25 * 16 = 4. Four being the answer to our 'what is 25% of 16' question.

Formula:  (p% ÷ 100) × X = Y

Example:  (25 ÷ 100) × 16 = 4

How to do I calculate the percentage of one number vs another number?

Lets say we want to work out what percentage is 50 out of 80. We can calculate 50 divided by 80 (which gives us 0.625) and then multiple by 100 (0.625 x 100) giving us 62.5%

Formula:  (X ÷ Y) × 100 = P%

Example:  (50 ÷ 80) × 16 = 62.5%

How do I calculate the percentage change between two numbers?

If we want to work out the percentage change (the increase or decrease) between two numbers, we would first deduct the original value from the new value, then divide the remainder by the original value and multiple by 100 to get our answer as a percentage. So lets say the intiial value is 65 and the new value is 70. We would deduct 65 from 70 leaving 5 remaining, then divide 5 by 65 giving us 0.0769 then multiply 0.0769 by 100 to give us a 7.69% increase.

Formula:  (Y - X) ÷ X × 100 = P%

Example:  (70 - 65) = 5,  5 ÷ 65 = 0.0769,  0.0769 × 100 = 7.69%