Using the supplied equivalence, 1 inch equals _____ centimetres.

### Why this is right The material states the conversion factor directly: $1$ inch equals $2.5$ centimetres. Multiplying an inch measurement by $2.5\ \text{cm}/\text{inch}$ converts the unit to centimetres. ### The concept A conversion factor is a ratio equal to one because its numerator and denominator describe the same length. When the factor is arranged correctly, the original unit cancels and the target unit remains. For example, $10\ \text{in}\times 2.5\ \text{cm}/\text{in}=25\ \text{cm}$. ### Worked numbers - **Given**: $1\ \text{in}$. - **Find**: centimetres. - **Convert**: $1\ \text{in}=2.5\ \text{cm}$. - **Answer**: $2.5\ \text{cm}$. - **Check**: inches cancel, leaving centimetres. ### Terms - **Inch (in)**: a unit of length used in the exercise. - **Centimetre (cm)**: a metric unit of length. - **Conversion factor**: a ratio used to express the same quantity in another unit. ### Remember Arrange the conversion factor so the unwanted unit cancels.