1) First off, you are going to need to have the same unit (either cm or mm). I used millimeters for this problem. 25cm=250mm
2) This next part is very easy to get wrong. You need to figure out what you are dividing, and by what. Simply look at the problem. <span><em>"How much longer is the guinea pig than her fish?" </em>This shows what numbers you should be getting. The guinea pig is 250mm long, where the fish is only 40. This means that her guinea pig should be larger. 250÷40=6.25
If youdid this problem the other way, you would've ended up with .16. If you put the sizes into perspective, you will notice that this is highly unlikely.
I hope that I have been able to simplify this problem for you!
