Project Maths: Probability teaser. (help)

Stalin and rugby

Sup tweeps been on this for ages so any help is appreciated. Q 7. pg 127 in the blue project maths book

"In an examination a candidate is required to select any 7 questions from ten.

(i) In how many ways can this be done?
(ii) How many of the selections contain the first and second questions?
Now calculate the probability that the candidate selects

(iii) both the first and second questions.
(iv) at least one of the first to questions.

Answers 120 , 56 , 7/15 , 14,15 ,

BeanbagBallbag

How many selections don't contain the first two?
How many contain just 1st without 2nd?
How many contain just 2nd without 1st?

The number of combinations left after you take out those is how many contain both 1st + 2nd. Try it that way.

Local_Chap

Is the answer to (i) 720 and (ii) 336

FaoiSin

Think that's it for part (ii)

reznov

Automatically, we choose two questions so out of a possible 10 we have 8 remaining.
Since we need to answer 7 questions, out of the remaining 8 choose any 5. (Guy in question is a newb because he couldn't answer all 10, but that's irrelevant)
And we have the answer of 56.

FaoiSin

Part (iii) and (iv) ... I've gotten rusty on these...

Stalin and rugby

YeaaahFaoiSin wrote: »

Part (iii) and (iv) ... I've gotten rusty on these...

By the looks of things you have not

FaoiSin

Despise this kind of Math

ConorSTF

The answer to the first part of the question is 120.

There are 10 options, you choose 7 = 10C7 = 120.

That's all my brain is up for at the moment, although I am off to study Probability now.