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X.1 Add and subtract numbers - up to two digits

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What are mixed operations with two-digit and one-digit numbers?

Mixed operations are math problems where you add or subtract. In this lesson, we will focus on problems with a two-digit number and a one-digit number.

Examples:
  • 56 + 7
  • 43 − 5
Note

You will always start with a two-digit number and then add or subtract a smaller one-digit number.

How do we solve addition problems with two-digit and one-digit numbers?

To add, use place value, counting on, or breaking apart the smaller number.

Steps:
  • Start with 56 + 7.
  • Break apart 7 into 4 and 3.
  • Add 56 + 4 = 60.
  • Then add the 3 left over: 60 + 3 = 63.
Note

Breaking apart numbers makes it easier to add to a “friendly number” like 60, 70, or 80.

How do we solve subtraction problems with two-digit and one-digit numbers?

To subtract, use place value, counting back, or breaking apart the smaller number.

Steps:
  • Start with 43 − 5.
  • Take away 3 first: 43 − 3 = 40.
  • Now take away the 2 left over: 40 − 2 = 38.
Note

Breaking apart the smaller number helps when subtracting to reach a “friendly number” like 40, 50, or 60.

Examples in sentences

We can use addition and subtraction in real-world problems to understand how they work in daily life.

Examples:
  • “I have 56 marbles. My friend gives me 7 more.” → 56 + 7 = 63.
  • “I have 43 apples. I eat 5 of them.” → 43 − 5 = 38.
Note

Always ask yourself: Am I adding to make the number bigger, or subtracting to make the number smaller?