Compare the fractions 3/2 and 2 4/5 by converting them to decimals.

Assuming "2.1" is a poorly written "2" for the mixed number $2\frac{4}{5}$:

$$2\frac{4}{5} = 2 + \frac{4}{5} = 2 + 0.8 = 2.8$$

Since 1.5 is less than 2.8, the correct symbol is '<'.

$$\frac{3}{2} < 2\frac{4}{5}$$

The symbol to fill in the box is $<$.