A number bond has a whole of 5. One part is 4. What is the other part?
A4 — the two parts should match each other
B1 — because 4 + 1 = 5
C9 — because you add 4 and 5 together
D0 — because nothing has been added yet
In a number bond, the two parts must always add up to the whole. Since the whole is 5 and one part is 4, the other part must be 1, because 4 + 1 = 5. The most common mistake is thinking the parts should match (option A) or confusing the parts with the whole (option C).
Question 2 Multiple Choice
Which of the following is NOT a valid way to break 5 into two parts?
A2 and 3
B1 and 4
C2 and 4
D0 and 5
In a number bond, the two parts must add up to the whole. 2 + 4 = 6, not 5, so this pair cannot be parts of 5. All other options check out: 2 + 3 = 5, 1 + 4 = 5, and 0 + 5 = 5. The key rule is that the parts always add back to the whole.
Question 3 True / False
Swapping the two parts of a number bond (for example, writing 3 + 2 instead of 2 + 3) gives you a different total.
TTrue
FFalse
Answer: False
Swapping the parts does not change the total. Whether you have 2 red apples and 3 green apples, or 3 green apples and 2 red apples, you still have 5 apples. The order of the parts does not matter — the whole stays the same. This is one of the first glimpses of the commutative property of addition.
Question 4 True / False
The number bond 5 = 4 + 1 and the number bond 5 = 1 + 4 describe the same relationship between the whole and its parts.
TTrue
FFalse
Answer: True
Both bonds have the same whole (5) and the same two parts (4 and 1). Swapping the positions of the parts doesn't create a new bond — it's the same parts combined in a different order, still equaling the same whole.
Question 5 Short Answer
What does it mean for two numbers to be 'parts' of 5, and why must the parts always add up to 5?
Think about your answer, then reveal below.
Model answer: Two numbers are 'parts' of 5 when they together make the whole of 5. They must add up to 5 because the parts come from the whole — you are splitting 5 into pieces, and no matter how you split it, all the pieces together must equal the original amount.
The part-part-whole relationship is the core idea: a whole number can be broken into pieces (parts), and those pieces always reassemble into the original whole. If the parts added to something other than the whole, you would have lost or gained objects — which is impossible when you're just rearranging. This is why every number bond is a balanced equation.