Now you can practice more types of mental math at the Math Mammoth online practice section. 😄 We've added various types of exercises for adding & subtracting two-digit numbers mentally , mostly matching what is taught in Math Mammoth curriculum, in grades 1-2. For example, children can practice adding a two-digit number and a single-digit number WITH or WITHOUT regrouping... e.g. 45 + 3 is without regrouping, but 45 + 8 is with regrouping. Or they can practice adding/subtracting multiples of ten (56 - 30 or 34 + 60). See more examples in the image above! Here's the link for the online practice page (and it's AD-FREE, plus not made with Flash): Two-digit addition & subtraction practice – mental math .