Skill: Use conversion factors

A conversion factor is a fraction equal to $1$ because its numerator and denominator name the same amount. For example,

$$1\text{ m}=100\text{ cm}$$

so both $\frac{100\text{ cm}}{1\text{ m}}$ and $\frac{1\text{ m}}{100\text{ cm}}$ equal $1$.

To convert, multiply by the factor that makes the old unit cancel.

Example: Convert $2.5$ meters to centimeters.

1. Start with the measurement:

$$2.5\text{ m}$$

2. Choose a conversion factor with meters on the bottom, so $\text{m}$ cancels:

$$\frac{100\text{ cm}}{1\text{ m}}$$

3. Multiply and cancel the meters:

$$2.5\text{ m}\times\frac{100\text{ cm}}{1\text{ m}}$$ $$=2.5\times100\text{ cm}$$

4. Calculate:

$$=250\text{ cm}$$

Therefore,

$$\boxed{2.5\text{ m}=250\text{ cm}}$$

This answer is reasonable because centimeters are smaller than meters, so the number should get larger.