To convert the infant's weight from pounds and ounces to kilograms, we need to follow these steps:
- Convert the weight in pounds and ounces to total ounces.
- Convert the total ounces to kilograms using the conversion factor (1 ounce = 0.0283495 kilograms).
- Round the result to the nearest tenth.
First, we convert the weight from pounds to ounces. Given that 1 pound is equal to 16 ounces, we have:
\[
9 \, \text{lb} \times 16 \, \frac{\text{oz}}{\text{lb}} = 144 \, \text{oz}
\]
Next, we add the additional 4 ounces to the total ounces:
\[
144 \, \text{oz} + 4 \, \text{oz} = 148 \, \text{oz}
\]
We then convert the total ounces to kilograms using the conversion factor \(1 \, \text{oz} = 0.02835 \, \text{kg}\):
\[
148 \, \text{oz} \times 0.02835 \, \frac{\text{kg}}{\text{oz}} = 4.1957 \, \text{kg}
\]
Finally, we round the result to the nearest tenth:
\[
4.1957 \approx 4.2
\]