The numbers in the list increase by 4 each time.
We can find the number of terms by finding the common difference and using the formula for the nth term of an arithmetic sequence.
The first term is 1.5 and the last term is 45.5.
The common difference is 4.
The nth term is given by $a_n = a_1 + (n-1)d$, where $a_1$ is the first term, $d$ is the common difference, and $n$ is the number of terms.
We can solve the equation $45.5 = 1.5 + (n-1)4$ for $n$ to find the number of terms.
Simplifying, we have $44 = 4n - 4$.
Adding 4 to both sides, we have $48 = 4n$.
Dividing both sides by 4, we have $n = 12$.
There are $\boxed{12}$ numbers in the list.
The answer is: 12
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
How many numbers are in the list $$ 1.5, 5.5, 9.5, 13.5, \ldots, 41.5, 45.5? $$

### Answer:
