Hello my name is Sue, my son came home with this problem this week(Grade 3). I need to show him in a simple way how i got my answer(11-6-4) i think Problem: Renee is 5 years older than Paulo. she is also 7 years older than Peter. The sum of their ages is 21. How old is each person. can you show me how i can explain this on paper to him thank you Sue Hi Sue, I think the technique to use here is guess-and-check. Renee must be at least 7 since she is 7 years older than Peter. They can't be very old since the sum of their ages is only 21. What if Renee is 9? If Renee is 9 then Paulo is 5 years younger so he is 4. Peter is 7 years younger so he is 2. Thus the sum of their ages is  9 + 4 + 2 = 15 The sum of their ages is too small so they must be older. So, what if Renee is 12? If Renee is 12 then Paulo is 5 years younger so he is 7. Peter is 7 years younger so he is 2. Thus the sum of their ages is  12 + 7 + 5 = 24 This time the sum of their ages is too large. Thus Renee must be 10 or 11. I think the point here for your son is that if he knows Renee's age he can find the ages of Paulo and Peter, and that if the sum of the ages is too small then Renee must be older and if the sum is too large Renee must be younger. I hope this helps, Penny Go to Math Central