Exam questions often ask for a percentage change using values read from a graph or table.percentage change = (new value − original value) ÷ original value × 100
A positive answer is a percentage increase and a negative answer is a percentage decrease.Example: the mass of a potato cylinder changed from 2.50 g to 2.20 g in a sucrose solution.Percentage change = (2.20 − 2.50) ÷ 2.50 × 100 = −12%.Percentage change is used instead of the actual change when the starting values are different, because it allows a fair comparison. For example, potato cylinders of different starting masses can be compared.Always divide by the original value, not the new value, and give the answer to a sensible number of significant figures.
A positive answer is a percentage increase and a negative answer is a percentage decrease.Example: the mass of a potato cylinder changed from 2.50 g to 2.20 g in a sucrose solution.Percentage change = (2.20 − 2.50) ÷ 2.50 × 100 = −12%.Percentage change is used instead of the actual change when the starting values are different, because it allows a fair comparison. For example, potato cylinders of different starting masses can be compared.Always divide by the original value, not the new value, and give the answer to a sensible number of significant figures.