You know that 6 + 4 = 10. Which of the following is a number bond to 20 you can figure out directly from this fact?
A16 + 4 = 20 only
B6 + 14 = 20 only
CBoth 16 + 4 = 20 and 6 + 14 = 20
DNeither — you need to memorize new facts for bonds to 20
Adding 10 to either partner of a bond to 10 gives a bond to 20. 6 + 4 = 10, so 16 + 4 = 20 (add 10 to 6) and 6 + 14 = 20 (add 10 to 4). Both work because 10 + 10 = 20. This mirror structure means every bond to 10 produces two bonds to 20 — no separate memorization needed.
Question 2 Multiple Choice
What number goes with 13 to make 20?
A7 — because 13 + 7 = 20, which mirrors 3 + 7 = 10
B3 — because 13 ends in 3
C17 — because bonds often pair numbers close to 20
D8 — the next number after 7
The bond-to-10 partner of 3 is 7. Since 13 = 10 + 3, the bond-to-20 partner is still 7 (the ones digit stays the same). 13 + 7 = 20. Option B confuses the digit inside 13 with the answer. The key insight: you never need to recalculate from scratch — the ones digit of your number tells you which bond-to-10 fact to use.
Question 3 True / False
If you know all the number bonds to 10, you already have the information needed to find every number bond to 20.
TTrue
FFalse
Answer: True
Every bond to 20 mirrors a bond to 10 with 10 added to one partner. For example, 3 + 7 = 10 becomes 13 + 7 = 20 or 3 + 17 = 20. There is no new set of facts to memorize — just a pattern to apply. This is why understanding the mirror structure matters more than rote memorization.
Question 4 True / False
Number bonds to 20 are twice as hard to learn as number bonds to 10 because there are twice as many new pairs.
TTrue
FFalse
Answer: False
Because every bond to 20 is derived from a bond to 10 (just add 10 to one partner), learning bonds to 20 requires recognizing a pattern, not memorizing a whole new set. The structure is identical; only the size of the numbers changes. Students who understand the mirror pattern can generate any bond to 20 instantly from bonds they already know.
Question 5 Short Answer
Explain how knowing 8 + 2 = 10 helps you find number bonds to 20.
Think about your answer, then reveal below.
Model answer: Adding 10 to either partner gives a bond to 20: 18 + 2 = 20 (add 10 to 8) or 8 + 12 = 20 (add 10 to 2). Both work because the original bond sums to 10 and 10 + 10 = 20, so the total increases by exactly 10.
This is the central insight of the topic: bonds to 20 aren't a new topic, they are bonds to 10 seen through a larger lens. Recognizing this mirror relationship is what separates students who can generate bonds to 20 flexibly from those who must memorize each pair separately.