Subtraction Within 20 — Answer Key
Part A: Multiple Choice
Circle the correct answer for each question.
1. A box has 16 crayons. You take out 9. How many are left in the box?
A) 5
B) 6
C) 7
D) 8
C is correct because 16 - 9 = 7, so 7 crayons are left.
2. Which number sentence is true?
A) 19 - 8 = 10
B) 17 - 9 = 8
C) 20 - 7 = 14
D) 16 - 5 = 10
B is correct because 17 - 9 = 8. The others are false: 19 - 8 = 11, 20 - 7 = 13, and 16 - 5 = 11.
3. If you know 7 + 8 = 15, which subtraction fact can you also know?
A) 15 - 6 = 9
B) 15 - 7 = 8
C) 15 - 9 = 6
D) 15 - 5 = 10
B is correct because 15 - 7 = 8 is the related subtraction fact from the fact family 7 + 8 = 15.
4. There were 20 balloons. Some popped. Now there are 13. How many popped?
A) 5
B) 6
C) 7
D) 8
B is correct because 20 - 13 = 7, so 7 balloons popped.
Part B: Fill in the Missing Number
Write the missing number to complete each number sentence.
1. 15 - 8 = 7
Since ___ - 8 = 7, the missing number is 8 + 7 = 15.
2. 18 - 9 = 9
Since 18 - ___ = 9, the missing number is 18 - 9 = 9.
3. 17 - 6 = 11
Since ___ - 6 = 11, the missing number is 6 + 11 = 17.
4. 20 - 15 = 5
Since 20 - ___ = 5, the missing number is 20 - 5 = 15.
5. 13 - 9 = 4
Since ___ - 9 = 4, the missing number is 9 + 4 = 13.