11 1/2 and 13 3/4 is?

This would depend on what you are asking for.

If you are adding the two numbers (which the word and is implying) you're answer is 25 1/4.

You get this by finding a common denominator. In this case, that can be 4.

Turn 1/2 in to 2/4.

Next, you add 11 and 13 to get 24.

Then, you'll add 2/4 and 3/4. You will get 1 1/4

Add 24 and 1 1/4. You have your answer of 25 1/4