Add `38.8+-0.4` and `29.7+-0.3`.

Explanation

To solve the problem of adding the two values \( 38.8 \pm 0.4 \) and \( 29.7 \pm 0.3 \), we can follow these steps:

### Step 1: Identify the values and their uncertainties
We have:
- Value \( a = 38.8 \) with uncertainty \( \Delta a = 0.4 \)
- Value \( b = 29.7 \) with uncertainty \( \Delta b = 0.3 \)

### Step 2: Add the central values
Now, we add the central values of \( a \) and \( b \):
\[ a + b = 38.8 + 29.7 \]
Calculating this gives:
\[ a + b = 68.5 \]

### Step 3: Add the uncertainties
Next, we need to combine the uncertainties. When adding two values with uncertainties, we add the absolute uncertainties:
\[ \Delta z = \Delta a + \Delta b = 0.4 + 0.3 \]
Calculating this gives:
\[ \Delta z = 0.7 \]

### Step 4: Write the final result
Now we can write the final result, combining the sum and the uncertainty:
\[ z = 68.5 \pm 0.7 \]

Thus, the final answer is:
\[ 68.5 \pm 0.7 \]

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