Four plus five plus six equals what?
We need to add together three numbers. We can add these numbers in any order. The total will stay the same. Do you notice anything about these two numbers, four and six or six and four? Six and four make 10. So first, we can add six and four to make 10. Now we just need to add the five. 10 plus five equals 15. Four plus five plus six equals 15. Six and four are a pair that make a 10. Then we add the five to make 15.