How many subjects do I need to prepare for a 90% chance of passing the exam?

[declan1]

I have a scenario where I have a list of 30 subjects that might appear in an online exam.

of the 30, only ten will actually appear in the exam and of those 10, I must select 5 to write a paragraph on.

Given that I have the list of thirty, how many paragraphs would I need to write in advance to ensure that I would have at least 5 of the selected 10?

I am having trouble calculating beyond the first event (each topic having a 1 in 3 chance of being part of the ten).

My instinct says 20, but I think it's likely less than that.

To clarify, my teacher says the learning outcomes are what is important, so having multiple paragraphs pre-prepared is not cheating.

 

[chisigma]

I have a scenario where I have a list of 30 subjects that might appear in an online exam.

of the 30, only ten will actually appear in the exam and of those 10, I must select 5 to write a paragraph on.

Given that I have the list of thirty, how many paragraphs would I need to write in advance to ensure that I would have at least 5 of the selected 10?

I am having trouble calculating beyond the first event (each topic having a 1 in 3 chance of being part of the ten).

My instinct says 20, but I think it's likely less than that.

To clarify, my teacher says the learning outcomes are what is important, so having multiple paragraphs pre-prepared is not cheating.

Wellcome on MHB delcan!...

... if You want to guarantee in the 'worst case', then You have to prepare at least 25 subjects... more complex but also much more interesting from the point of view of the calculus of probability would be, for example, calculate how many subjects to prepare for say .9 chance of passing the exam ...

Kind regards

$\chi$ $\sigma$

 

[declan1]

Wellcome on MHB delcan!...

... if You want to guarantee in the 'worst case', then You have to prepare at least 25 subjects... more complex but also much more interesting from the point of view of the calculus of probability would be, for example, calculate how many subjects to prepare for say .9 chance of passing the exam ...

Kind regards

$\chi$ $\sigma$

Thanks for that, I see what you've done. Simple now really. How about the 90% chance scenario. That would likely be much lower right? I like to live dangerously and have 2 of these exams to prep for. A 'good paragraph' answer being 300 words, that's 15000 words I need to write to guarantee a pass. There must be a high chance ratio that would bring down the writing volume considerably. There are probably a couple from the list of 30 I could also take a punt and say they won't be in the final 10. How would I calculate the 2 scenarios so I can work it out for myself?