Probability: making a sandwich from 7 ingredients

Hi I'm having trouble with this question!

You can choose from 7 different ingredients (a,b,c,d,e,f,g) when making a sandwich.

a) What is the probability that the sandwich contains ingredient "a"?

b) What is the probability that the sandwich contains three ingredients?

c) What is the probability it contains at least three ingredients?

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Hi galactus!! Thanks for the super fast response! I was wondering if this is a bernoulli or markov sequence? Thanks!

Re: Paucity Probability

seek_solutions said:

You can choose from 7 different ingredients (a,b,c,d,e,f,g) when making a sandwich.
What is the probability that the sandwich contains a?
What is the probability that the sandwich contains three ingredients?
What is the probability it contains at least three ingredients?

Click to expand...

This question is so imprecise as to almost be meaningless.
Let’s qualify it: we can choose at least one ingredient or at most all seven.

There are (2<SUP>7</SUP>-1) subsets of ingredients that contain at least one ingredient..
There are 2<SUP>6</SUP> subsets of ingredients that contain ingredient a.

There are combin(7,3) subsets that contain three ingredients.

There are 2<SUP>7</SUP>-1-combin(7,1)-combin(7,2) subsets of ingredients that contain at least three.

I see, I misinterpreted the problem.

galactus said:

I see, I misinterpreted the problem.

Click to expand...

I may not have given the correct reading!
That was just a guess as to what was intended.