Expand a Fraction

$$\frac{4}{5}=\frac{4\times 3}{5\times 3}=\frac{12}{15}$$

You have now expanded the fraction $\frac{4}{5}$ by $3$ and gotten $\frac{12}{15}$. If you input these two very different looking expressions into a calculator, it will tell you that both of them are equal to $0.8$. The fractions have the same value!