**Exercise 1.8**:

Let be the event that the number is divisible by 4,6, and 9; respectively.

It’s easy to calculate:

So the probability that the number chosen is divisible by one or more of 4, 6, and 9 is:

**Exercise 1.10**:

Let be the event that the chosen coin is fair, be the event it is two-headed; and let B is the event that the flip is head.

We have

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