On a certain highway, 7% of the vehicles have $18$ wheels, and the other 93% of the vehicles have $4$ wheels. (We ignore motorcycles, etc., for simplicity.) A child looks out the window and counts the wheels on the next vehicle to pass.
a. What is the expected number of wheels?
My work:
I'm not sure which interpretation is correct and would like it if someone could tell me which one is.
$E(X)$ where $X$ is the random variable that represents the number of wheels is $E(X) = 4 \cdot 0.93 + 18 \cdot 0.07 = 4.98$ wheels. Is this the correct interpretation? OR is $E(X) = p = 0.07$ where $p$ is the probability of a "success" (the kid sees a $18$-wheeler) the correct interpretation?
Thank You!