why does 4 / 0.5 =8?

would start by asking what is 4 * 0.5 ? They might then work out that that is 2 which would lead them to have a cognitive conflict which can be very useful as they can understand that the logic is wrong.

I would then use a diagram of 4 blocks to represent 4 and ask how many times 0.5 will go into it to reach the answer of 8