50% of 55 is 27.5. To calculate this, we can use the following steps:

1. Write 50% as 50/100.
2. Multiply 50/100 by 55 to get the answer.
3. Simplify the result if needed.

Using this method, we get:

50/100 * 55 = 0.5 * 55 = 27.5

Therefore, 50% of 55 is 27.5.