Answer is 2:1
Step-by-step explanation:
Here are the possible outcomes: {1,2,3,4,5,6}
We want a 2 or a 4 to happen, so the complement or opposite of those would be {1,3,5,6}
There are 4 things we don't want to happen {1,3,5,6} and 2 things we do want to happen {2,4}
The odds against rolling a 2 or 4 is 4:2 and that simplifies to 2:1
This is read out as "2 to 1". Meaning the stuff we don't want to happen will happen twice as likely compared to the outcomes we want to see.