how do you explain how 1/2-4 is the correct answer for the questions: What is 4 less than half a number

Answer 1

Suppose I am thinking of a number, let's say 14. What is half of that number? 1/2 of 14 is 7. Get used to the idea that "of" means multiply. Now what is 4 less than 7? To make a quantity less than it currently is means to subtract. In this case 4 less then 7 is 3.

Now suppose I do not tell you what the number is that I am thinking of. This is where we use a variable to represent the number I am thinking of. Let's use x. Now follow the same pattern we did when you knew the number, that is multiply by 1/2 and then subtract 4. So a possible correct answer is 1/2 (x) - 4. Note that your answer is missing the variable to represent the number.