Pairs of numbers which add together to make twenty: These are known as number bonds to twenty and are useful when calculating quickly. Once the addition facts, or number bonds, are learned by heart, children may then learn the associated subtraction facts. For example, if 17 + 3 = 20, then 20 - 3 = 17 or 20 - 17 = 3.
Join 4M+ learners. Unlock unlimited quizzes, wrong-answer tracking, flashcards + reminders, study guides, and 1-on-1 challenges.