Place Value Addition: Finding Number Pairs That Sum to 15

To determine which addition exercise using tens and units results in the number 15, follow these steps:

• Step 1: Understand the requirements. We are asked to use a combination of:

  • Tens (a multiple of 10).
  • Units (a single-digit number).
  to sum to 15.

• Step 2: Consider possible tens values. Starting from the smallest possible multiple of 10, which is 10, because 20 or more would exceed 15 when adding any units.

• Step 3: Calculate the necessary unit. Subtract the chosen tens value from the total desired sum: $15 - 10 = 5$ So, the necessary units value is 5.

• Step 4: Verify the calculation. Combining the tens and units adds up to: $10 + 5 = 15$

• Step 5: Confirm from choices. Among the given choices, $10 + 5$ is option number 1, and it meets our criteria correctly.

Therefore, the correct addition exercise using tens and units is $10 + 5$, resulting in the number 15.