Grade 2 Number Bonds: Number Bonds to 100

Find the two parts that make 100

What You'll Learn

Find the missing part that makes 100 (64 + ? = 100)
Connect to place value: the ones make 10 and the tens make 9 tens, or the tens alone make 10 tens

📖Bonds to 100

Every bond in this lesson makes 100. For 64 + ? = 100, the ones must make 10: 4 + 6 = 10. That ten joins the tens, so the tens must make 9 tens: 60 + 30 = 90. The missing part is 36, and 64 + 36 = 100. When there are no ones, only the tens work: for 30 + ? = 100, 3 tens + 7 tens = 10 tens, so the missing part is 70.

Worked examples

Real problems from the practice worksheets, solved one step at a time.

Example 1
80 + 20 = ?
1. A number bond joins two parts to make a whole. Here the two parts are 80 and 20.
2. To find the whole, put the parts together: 80 + 20.
3. So the whole is 100.
Answer: 100
Example 2
? + 79 = 100
1. A number bond joins two parts to make a whole. The whole is 100 and one part is 79.
2. To find the missing part, take the known part away from the whole: 100 − 79.
3. So the missing part is 21.
Answer: 21
Example 3
63 + ? = 100
1. A number bond joins two parts to make a whole. The whole is 100 and one part is 63.
2. To find the missing part, take the known part away from the whole: 100 − 63.
3. So the missing part is 37.
Answer: 37