Solve for the Missing Addend in 5.8 + ? = 9.9

To solve this problem, we need to determine the missing value in the equation $5.8 + ? = 9.9$.

• First, let's isolate the unknown value by rearranging the equation. We know that $? = 9.9 - 5.8$.
• Next, perform the subtraction: $9.9 - 5.8$.

Let's calculate:

Align the decimal places and subtract:

  9.9
- 5.8
-----
  4.1

The result of $9.9 - 5.8$ is $4.1$.

Therefore, the missing value is $4.1$. Hence, the equation becomes $5.8 + 4.1 = 9.9$.

Therefore, the correct answer is option 2: 4.1.