Answer:
0.25
Explanation:
We are given that Rob created the Venn Diagram shown below which gives us,
The probability of teenagers who like to eat hot dogs = P(HD) = 0.3
The probability of teenagers who like to eat hamburger = P(HB) 0.4
The probability of teenagers who like to eat both = P( HD ∩ HB ) =0.1
The probability of teenagers who like to eat none = 0.2
It is required to find the probability that a teenager eats hot dogs when it is given that he/she eats hamburger i.e. P( HD | HB ).
Now, we know that the probability that an event B occurs given that event A has already occurred is given by,

So,

i.e.

i.e.

Hence, the probability that a teenager eats hot dogs when it is given that he/she eats hamburger is 0.25.