Copy and complete (a) 1/4 = ?/8 (b) 3/4 = ?/8

To change the denominator from 4 to 8, we multiply by 2 ($4 \times 2 = 8$). We must do the same to the numerator.

$$\frac{1}{4} = \frac{1 \times 2}{4 \times 2} = \frac{2}{8}$$

So, the missing numerator is 2.

Again, to change the denominator from 4 to 8, we multiply by 2 ($4 \times 2 = 8$). We must do the same to the numerator.

$$\frac{3}{4} = \frac{3 \times 2}{4 \times 2} = \frac{6}{8}$$

So, the missing numerator is 6.

The completed fractions are:

a) $\frac{1}{4} = \boxed{\frac{2}{8}}$

b) $\frac{3}{4} = \boxed{\frac{6}{8}}$