Mental Math Within 100 — Answer Key
Part A: Sort the Words
Sort each word or number into the correct category box.
1. Sort each pair by whether it adds up to 10 or does not.
Makes 10
7 + 36 + 42 + 81 + 9 Does NOT make 10
5 + 64 + 5 Pairs like 7+3, 6+4, 2+8, and 1+9 all equal 10, but 5+6 is 11 and 4+5 is 9, so those do not make 10.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Use a number bond of 10 to finish: 8 + 2 = 10.
8 needs 2 more to get to 10, so the missing part of the bond of ten is 2.
2. To add 37 + 3 quickly, notice that 7 + 3 makes 10. The answer is 40.
37 has 3 tens and 7 ones, and adding 3 ones fills the next ten, making 40.
3. 52 + 8 uses 2 + 8 = 10, so the sum lands on 60.
52 plus 8 ones fills a full ten, moving from 50s into the next ten at 60.
4. 6 + 4 = 10, the bond of ten partner is the missing number.
6 and 4 are number bond partners because 6 + 4 equals exactly 10.
5. 74 + 6 equals 80 because 4 + 6 makes 10.
74 plus 6 ones makes a full ten, moving the sum up to the next decade, which is 80.
Part C: True or False?
Read each statement. Circle True or False.
1. 7 and 3 are number bond partners because together they make 10.
True False
7 plus 3 is 10, so the two numbers are a bond-of-ten partner pair.
2. Making tens helps you solve problems like 48 + 2 quickly.
True False
8 + 2 is 10, so 48 + 2 jumps to the next ten, 50, without long counting.
3. 5 and 6 are partners that make 10.
True False
5 plus 6 equals 11, not 10, so they are not a bond-of-ten partner pair.
4. Knowing number bonds of 10 has nothing to do with adding two-digit numbers.
True False
Bonds of 10 let you fill tens inside bigger numbers so sums like 36 + 4 become 40.