The table shows the number of cars and trucks that used a certain toll road on a particular day The number of cars and trucks that used, and did not use, an electronic toll pass on that same day was also recorded
\begin{tabular}{|c|c|c|r|}
\hline Toll Pass & Cars & Trucks & Total \\
\hline Used & 547 & 349 & 896 \\
Did not use & 960 & 648 & 1608 \\
\hline Total & 1507 & 991 & 2504 \\
\hline
\end{tabular}
a) If one of these vehicles is selected at random, determine the probability that the vehicle was a truck.
b) If one of these vehicles is selpcted at random, determine the probability that the vehicle was a truck, given that the vehicle did not use a loll pass

The probability that the vehicle was a truck is $\square$
(Round to four docimal places as needed)
The probability that the vehicle was a truck, given that the vehicle did not use a toll pass, is $\square$
(Round to four decimal places as needod)

Step 1 ：Given the total number of vehicles is 2504, the total number of trucks is 991, the number of trucks that did not use a toll pass is 648, and the total number of vehicles that did not use a toll pass is 1608.

Step 2 ：The probability that a randomly selected vehicle is a truck can be calculated by dividing the total number of trucks by the total number of vehicles. So, the probability is \(\frac{991}{2504} = 0.3957667731629393\).

Step 3 ：The conditional probability that a vehicle is a truck given that it did not use a toll pass can be calculated by dividing the number of trucks that did not use a toll pass by the total number of vehicles that did not use a toll pass. So, the probability is \(\frac{648}{1608} = 0.40298507462686567\).

Step 4 ：Rounding to four decimal places, the probability that the vehicle was a truck is \(\boxed{0.3958}\).

Step 5 ：The probability that the vehicle was a truck, given that the vehicle did not use a toll pass, is \(\boxed{0.4030}\).