RS Math: Tips for Mental Math

Hi Everyone, My husband came up with the following formula to help our second grader wean himself off the abacus or the white board when doing mental math. The following strategy is one we have been using when adding two two-digit numbers. Hopefully it will help someone else!I recommend starting on the white board for a few tries and then trying it without. Your student will probably be eager to do it in their head. Step one: Pick one of the two addends and add the tens from the other addend to this number. ex. 47 + 44 becomes 47+40= 87 You may choose to cross out the 47 and the 4 in the tens column so the child knows the numbers have already been used. Step two: Ask yourself: “What is the closest ten to my answer?” In our example it would be 90 Write the 90 down if you are using the white board. Step 3: Ask yourself: “What do I need to get to ninety? 3 Step 4: Where am I going to get that 3? From the leftover “ones”– In this case a 4 Step 5: How many ones are left? 1 Step 6: And so our answer is…voila!…. 91 I thought this sounded too complex but after just a few goes, ds is doing quite well with it. As long as he remembers all the steps. We have him say them out loud for now. Could be because he thinks just like his dad but I think the premise is consistent with RS math as we are focusing on making groups of ten. You also get a little subtraction practice too:) Hope this helps! Jennifer