Round the value 28.5 off to 2 significant digits.

The given value is $28.5$.

We need to round it off to $2$ significant digits.

The digit to be dropped is $5$.

According to the rules of rounding off, if the digit to be dropped is $5$ and is not followed by any non-zero digit, the preceding digit is left unchanged if it is even, and is increased by $1$ if it is odd.

Here, the preceding digit is $8$, which is an even number.

Therefore, the value $28.5$ is rounded off to $28$.