- Aand are independent.
- Band are independent.
- Cand are independent.
- Dand are independent.
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Correct answer: D
- Sample space and basic probabilities
When two fair six-faced dice and are thrown simultaneously, the total number of equally likely outcomes is
We define:
- : die shows
- : die shows
- : sum on the two dice is odd
So, because if die , die can be anything.
Similarly,
Now for : The sum is odd when one die is odd and the other is even. Each die has odd and even faces, so P(E_3)=\frac{3\cdot 3+3\cdot 3}{36}=rac{18}{36}=rac{1}{2}.
- Check option A: and are independent
We compute: since this is the single outcome .
Also,
Thus, so and are independent.
Hence, A is true.
- Check option B: and are independent
If occurs, then die (which is even). For the sum to be odd, die must be odd: . So favorable outcomes are: which are outcomes.
Therefore,
Now,
Thus, so and are independent.
Hence, B is true.
- Check option C: and are independent
If occurs, then die (which is even). For the sum to be odd, die must be odd: . So favorable outcomes are: which are again outcomes.
Therefore,
And,
Thus, so and are independent.
Hence, C is true.
- Check option D: are independent
For three events to be independent, we need:
- pairwise independence, and
We already found pairwise independence above.
Now check the triple intersection:
- means
- means So together this gives the outcome only. But then the sum is which is even, not odd. Hence, and therefore
But
So the three events are not mutually independent.
Hence, D is false.
- Conclusion
The statement which is NOT true is:
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