All Operations in Decimal Fractions: Simple addition

To solve this problem, we will perform the following steps:

• Step 1: Align the decimal numbers so the decimal points are vertically in line. The numbers are $10.1$ and $2.3$.
• Step 2: Add the numbers starting from the rightmost column (i.e., the tenths place), moving to the left.

Let's perform the addition:

$\begin{array}{c} 10.1 \\ + 2.3 \\ \hline \end{array}$

Starting from the right, we add the digits in the tenths place: $1 + 3 = 4$.

Next, add the digits in the units place: $0 + 2 = 2$.

Finally, add the digit in the tens place: $1 + 0 = 1$.

Therefore, the result of adding $10.1 + 2.3$ is:

$12.4$

We can verify that this matches with the given answer choices. The correct choice is:

Option 1: $12.4$

To solve this problem, we'll follow these steps:

• Step 1: Align the numbers 2.5 and 3.1 by their decimal points.
• Step 2: Add the digits in each column starting from the rightmost digit (the tenths column in this case).

Now, let's work through each step:

Step 1: Align the numbers by decimal points:

$\phantom{00}2.5$
$+3.1$

Step 2: Perform the addition:
- Add the tenths column: $5 + 1 = 6$
- Add the units column: $2 + 3 = 5$

Therefore, by aligning and adding the numbers correctly, the solution to the problem is $5.6$.

To solve this problem, let's follow these steps for decimal addition:

• Step 1: Align the decimals of the numbers vertically, so that both $5.1$ and $2.3$ have their decimal points in the same position:

   5.1
+  2.3
---------

• Step 2: Start adding from the rightmost column (the tenths position). Add the tenths: $1 + 3 = 4$.
• Step 3: Move to the left to add the units: $5 + 2 = 7$.

Put these sums together, and we have:

   5.1
+  2.3
---------
   7.4

Therefore, the sum of $5.1$ and $2.3$ is $7.4$. This matches choice $\text{3}$.

Thus, the correct answer is $7.4$.