What is the average number of Dell Laptops sold by stores, P R and S together?

Answer: Option B

Percent of Dell Laptops sold by P, R and S together
= 15% + 30% + 9%
= 54%
Total Dell Laptops sold by P, R and S together
$$\begin{array}{rl}& =2400\times \frac{54}{100}\\ & =1296\\ & \therefore \text{ Average}\\ & =\frac{1296}{3}\\ & =432\end{array}$$