- #1
Poopsilon
- 294
- 1
Homework Statement
If a 3-digit number (000 to 999) is chosen at random, find that probability that exactly 1 digit will be >5
The Attempt at a Solution
So basically I first look at the probability of at least 1 digit being greater than 5, taking into account multiple counting:
P(A ∪ B ∪ C) = P(A) + P(B) + P(C) - P(A ∩ B) - P(A ∩ C) - P(B ∩ C) + P(A ∩ B ∩ C).
Now the part where I'm a bit confused, I need to now subtract the probability of having at least two digits greater than 5. I'm inclined make the subtraction:
-[P(A ∩ B) + P(A ∩ C) + P(B ∩ C) + P(A ∩ B ∩ C)].
But now I'm afraid I've done some multiple counting again and so finally add:
3P(A ∩ B ∩ C)
This comes out to: 3(4/10) - 6(16/100) + 3(64/1000) = .372
Yet the back of the book is saying .432, where have I gone wrong? Thanks.