If the number begins by being rational, multiplying by 0.5 will not change whether or not it is rational. It will remain rational.
That would include any even number 12 * 0.5 = 6
12 started out as rational, so the answer is rational (6)
Any odd number is also rational
23 * 0.5 = 11.5
23 and 11.5 are both rational.
3.636363636 ... is rational so when multiplied by 0.5 the result will be rational.
1.818181818....
So if we start with something irrational like pi
then pi * 0.5 is not rational.
If you have choices, please list them.