TestTaker0
Is it right to use the sum formula here?
Total = A + B - both + neither
So I got: 1 = 0.2 + 0.4 - 0 + Neither
Neither = 0.4
Therefore, I thought, either A or B is the opposite of neither, so 1 - 0.4 = 0.6 or 3/5
My answer is therefore correct but did I do it right? E.g. is it right to assume that Total = 1 ?
TestTaker0Yes, your approach is correct. Let me validate your method and explain why it works perfectly for this problem.
Your Formula is Valid The formula you used (Total = A + B - both + neither) is indeed correct, though it's more commonly written as: \(1 = P(M \text{ only}) + P(R \text{ only}) + P(\text{both}) + P(\text{neither})\)
This is the fundamental principle that all possible outcomes in a probability space must sum to 1.
Why Total = 1 is Correct Yes, assuming Total = 1 is absolutely right! Here's why:
- In any probability problem, the sum of all mutually exclusive and exhaustive outcomes equals 1
- The four scenarios (M only, R only, both M and R, neither M nor R) cover every possible outcome
- Since these four scenarios account for 100% of possibilities, their probabilities must sum to 1
Alternative Verification:
You could also use the standard addition rule: \(P(M \text{ or } R) = P(M) + P(R) - P(M \text{ and } R) = 0.2 + 0.4 - 0 = 0.6\)
Both methods give the same answer.