Complements to 10

Mental Math · Axiom Academy

Every digit has a partner that finishes a ten. Learn the five pairs and awkward sums start clicking into round, easy numbers. 1. The Partner That Finishes a Ten Picture a ten-frame — ten little boxes. Put 7 counters in and three boxes stay empty. That gap, 3 , is the complement of 7: the exact amount that finishes the ten. Every number from 0 to 10 has one. 2. Five Pairs Cover Everything You do not memorize ten separate facts — there are really just five pairs , and they are symmetric. Read them once forward and you already know them backward: 9 with 1 is the same partnership as 1 with 9. 3. Make a Ten, Then Add the Rest Here is why partners matter. To add 8 + 7 , look at the 8 — it is just 2 short of ten. Borrow 2 from the 7 (splitting it into 2 + 5 ), snap that 2 onto the 8 to make a clean 10, and the leftover 5 gives you 15 . For 9 + 6 , the 9 needs only 1. Split the 6 into 1 + 5, complete the ten, and add the leftover 5: The question is always the same: how far is the bigger number from ten? That distance is the piece you pull from the other number. 4. Spot the Pairs Hiding in a Sum When several numbers line up, scan for partners first . In 8 + 7 + 2 , the 8 and the 2 are complements — snap them into a 10, then the 7 rides along to make 17 . Rearranging is always allowed; addition does not care about order. glance across the numbers for any two that make ten (here 8 and 2) — combine those before you touch the rest.

This is the written version of the interactive lesson above. See the full Mental Math course.