Final answer:
The probability that a student goes to the library to check out a book or a DVD can be calculated using the formula P(B or D) = P(B) + P(D) - P(B and D). Given the values P(B) = 0.40, P(D) = 0.30, and P(B and D) = 0.20, the probability is 0.50.
Step-by-step explanation:
The probability that a randomly chosen student goes to the library to check out a book or a DVD can be calculated using the formula P(B or D) = P(B) + P(D) - P(B and D).
Given that P(B) = 0.40, P(D) = 0.30, and P(B and D) = 0.20, we can substitute these values into the formula and calculate the probability:
P(B or D) = 0.40 + 0.30 - 0.20 = 0.50