The answer you are looking for is 2.5.
To find this answer, you first have to subtract 5 from 10 since the question asks "1/2 of 5 less than 10" which means 10 - 5. This will give you 5, which you then divide by 2 (to find the "1/2" portion of what the question is asking" and get your final answer. Thus making 2.5 the answer.
I hope this helps!