问题及解答

An automobile service facility specializing in engine tune-ups knows that $45\%$ of all tune-ups are done on four-cylinder automobiles, $40\%$ on six-cylinder automobiles, and $15\%$ on eight-cylinder automobiles. Let $X=$ the number of cylinders on the next car to be tuned.

• (a) What is the pmf of $X$?
• (b) Draw both a line graph and a probability histogram for the pmf of part (a).

Remark. Here pmf stands for probability mass function.

The pmf is 

for $x\neq 4, 6, 8$, $p(x)=0$.