To determine the number of bacteria in an 18-gram sample based on the information given for the 11-gram sample, we first need to calculate the bacteria density (bacteria per gram) in the 11-gram sample:
\[ \text{Bacteria density} = \frac{7.5 \times 10^7 \text{ bacteria}}{11 \text{ grams}} \approx 6.81818 \times 10^6 \text{ bacteria/gram} \]
Next, we can multiply this density by the weight of the new sample (18 grams) to find the total number of bacteria:
\[ \text{Total bacteria in 18 grams} = 6.81818 \times 10^6 \text{ bacteria/gram} \times 18 \text{ grams} = 1.227273 \times 10^8 \text{ bacteria} \]
To express this result in scientific notation, we round \(1.227273 \times 10^8\) to three significant figures:
\[ \approx 1.23 \times 10^8 \]
Thus, the number of bacteria in an 18-gram sample is approximately \(1.23 \times 10^8\).