Unit 2 Contents

1. What strategies can you use to solve 16 − 9?
2. What strategies can you use to solve 16 − 7?
3. What strategies can you use to solve 18 − 10?
4. Fern used addition to help her find the answer to a subtraction fact. She said, “5 + 9 = 14.” What subtraction fact or facts can she solve using this addition fact?
5. Roberto is trying to find the answer to 15 − 6. He counts up and says, “from 6 to 10 is 4 and from 10 to 15 is 5.” How could he use these numbers to help him solve the fact 15 − 6? Explain.
6. Sam said, “I know 5 − 2 = 3. I don't use any strategy for that fact. I just know it!” Name three subtraction facts you just know.

Thinking Addition

Thinking addition can help you solve a subtraction problem and it can also help you check your answer. John thought about solving the problem below.

15 − 8 =

“I was pretty sure that 15 − 8 is 7, but I checked it in my head,” said John. “I started with 7 and added 8. Since 7 + 8 = 15, I knew my answer was right.”

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“I check all my subtraction problems,” said Suzanne. “Adding is the opposite of subtraction. If I subtract and then add the same number back, I know I was right if I get back what I started with. Thinking addition helps me check my subtraction.”