# Thread: Probability question that I cant work out

1. ## Multiple attempt percentages

Hi all,
I answered questions from set A and was correct 64% of the time. Every time I was incorrect I had to answer a different set of questions (set B) and of these I was correct 66% of the time. When I was incorrect with a question from set B I had to answer a question from set C of which I was correct 70% of the time.

I was wondering what the probability of getting all three questions wrong is?
How many questions would I get correct from set A,B and C before I got all three wrong (on average)?
How many times would I expect to get all three answers wrong if I answered 1000 questions from set A?

Thanks so much for your help!

2. ## Re: Multiple attempt percentages

So I've been going through all the treads trying to find something that may help me. Is it Binomial probability that I would need to use to find the answer?
Sorry for my ignorance... math was never my strong point!!

3. ## Re: Multiple attempt percentages

Originally Posted by tjcoll
Hi all,
I answered questions from set A and was correct 64% of the time. Every time I was incorrect I had to answer a different set of questions (set B) and of these I was correct 66% of the time. When I was incorrect with a question from set B I had to answer a question from set C of which I was correct 70% of the time.

I was wondering what the probability of getting all three questions wrong is?
How many questions would I get correct from set A,B and C before I got all three wrong (on average)?
How many times would I expect to get all three answers wrong if I answered 1000 questions from set A?

Thanks so much for your help!
The probability of getting all three wrong is (1-0.64)(1-0.66)(1-0.70)

CB

4. ## Re: Multiple attempt percentages

Great, thanks!!