A.0.3—Ratios, fractions and percentages

A ratio compares quantities on the same basis; a percentage expresses a part relative to a stated whole. Keep the order of the ratio explicit before calculating.

Simplify a ratio only after converting units. For a percentage change, divide the change by the original value, not the final value.

If a culture rises from 40 to 50 cells, the increase is 10/40 × 100 = 25%, whereas the new value is 125% of the original.

A ratio of 2:1 is not the same claim as “twice as many” unless the numerator and denominator are clearly defined.