It's back to fractions, and today we're adding and subtracting them. It sounds very complicated, but it boils down to one simple rule - leave the denominator alone!
Here, I've got 2/8 and underneath, 5/8.
If I add all of those yellow bits up, look what we get;
7/8! That they are still chopped up into 8 bits hasn't changed, we've just got more of them. In this case, 2 + 5 = 7. The exact same is true for taking away - if I took away 2/8 from 7/8 I'd get 5/8. The bottom number doesn't go anywhere!
Have a look at this BBC Bitesize clip for more on leaving that bottom number as it is. Don't take away or add the bottom number. It's just the top number, the numerator. But the bottom number, the denominator? You don't change it. At all. Right?
Once you've wrapped your head around that, log on to Mathletics and adding and subtracting fractions. Good luck!