You are Here: Home >< Maths

# S1: Probability Distribution watch

1. Our maths teacher said in order to do this question - just draw the whole tree diagram and add all the probabilities. The problem with this is that it would take far too long. And I read you can use combination to solve this. Problem is my permutation and combinations is really bad so I can't really grasp the concept here. Can someone explain it? (I already have the answer but I just want explanations for the steps including combination)
2. each probability is the number of ways of choosing n number of girls/ number of ways of choosing 4 people from a group of 8.

For example; for there to be 3 girls there has to be 1 boy. So the number of ways of choosing 3 girls is

All the possible combinations of 4 from 8 are

So the number of ways of choosing 3 girls is
3. (Original post by NotNotBatman)
each probability is the number of ways of choosing n number of girls/ number of ways of choosing 4 people from a group of 8.

For example; for there to be 3 girls there has to be 1 boy. So the number of ways of choosing 3 girls is

All the possible combinations of 4 from 8 are

So the number of ways of choosing 3 girls is
...but there are 5 girls and 3 boys to choose from, so isn't it

?
4. (Original post by old_engineer)
...but there are 5 girls and 3 boys to choose from, so isn't it

?
Yes, that's what I meant (read it incorrectly) . I'll edit the post to reflect this. The mark scheme should have the same answer.

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: February 17, 2018
Today on TSR

### Top unis in Clearing

Tons of places at all these high-ranking unis

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams