Probability question

[Diver]

There's an excellent probability that I may never read this Boring Tulip thread again

[tay]

SAS is a student trolling for answers to his assigment, and I claim my 5 free course credits.

[sasguru]

SAS is a student trolling for answers to his assigment, and I claim my 5 free course credits.

Thankfully I won't ever have to do an exam again. Problems like this niggle at me though.

[tay]

But because I am generous I shall use my super large brain to provide the answer.

the answer is 4

Look at the results

TT,TF,TI, FT,FF,FI, IT,IF,II

where T is a correct answer

no look at the question very carefully ..

What is the probability of exactly one correct answer?

So that leaves these

TT,TF,TI, FT,FF,FI, IT,IF,II

Four.

[sasguru]

But because I am generous I shall use my super large brain to provide the answer.

the answer is 4

Look at the results

TT,TF,TI, FT,FF,FI, IT,IF,II

where T is a correct answer

no look at the question very carefully ..

What is the probability of exactly one correct answer?

So that leaves these

TT,TF,TI, FT,FF,FI, IT,IF,II

Four.

[tay]

Hth

Even I make me laugh sometimes.

[TimberWolf]

The actual answer is 4/9. But I can't work out why.
Your sample space is of course correct.

Maybe it's a trick question related to the 'insufficient data' criteria (which is neither true or false), and there are four possible combinations of those: TT, TF, FT, FF, whereas the random picker has a choice of 9 combinations, of which only four can be correct.

[sasguru]

Maybe it's a trick question related to the 'insufficient data' criteria (which is neither true or false), and there are four possible combinations of those: TT, TF, FT, FF, whereas the random picker has a choice of 9 combinations, of which only four can be correct.

No I think insufficient data can be a valid answer.

[TimberWolf]

Okay, here's another way of thinking about it.

He can only get one right in total by either getting the first one right (1 in 3 chance) and the second one wrong (2 in 3) or ditto but reversed.

So the probabilty of getting just one right is 1/3 * 2/3 + 2/3*1/3 = 4/9

[thunderlizard]

I did it TimberWolf's way