You are Here: Home >< Maths

# probability at most one event occur?

Announcements Posted on
Last day to win £100 of Amazon vouchers - don't miss out! Take our quick survey to enter 24-10-2016
1. this person has 20 ties

2 red 3 blue 15 mixed colours
he selects 2

find the probability that at most one is red
Spoiler:
Show
trying to help a friend but i forgot the method :-s
2. (Original post by ihatePE)
...
Hint: Does 1 - probability (of something) ring a bell for you?
3. (Original post by Zacken)
Hint: Does 1 - probability (of something) ring a bell for you?
it does but elaborate?

1 - 2/20?? i tend to forget everything after exams :s
4. (Original post by ihatePE)
it does but elaborate?

1 - 2/20?? i tend to forget everything after exams :s
Find the probability that they are both red. Then 1 - that is the probability that they are not both red, which is the same as saying that either none or one is red which is the same as saying that at most one is red.
5. (Original post by Zacken)
Find the probability that they are both red. Then 1 - that is the probability that they are not both red, which is the same as saying that either none or one is red which is the same as saying that at most one is red.
so 1 - 4/40?

or 1 - 1/10?
i feel so dumb
6. (Original post by ihatePE)
so 1 - 4/40?

or 1 - 1/10?
i feel so dumb
He has twenty ties. He picks two, the probability that the first one is red is 2/20. The probability that the second one is red is 1/19.

The probability that he gets two reds is then 2/20 * 1/19.
7. (Original post by Zacken)
He has twenty ties. He picks two, the probability that the first one is red is 2/20. The probability that the second one is red is 1/19.

The probability that he gets two reds is then 2/20 * 1/19.
so 1 - (2/20 * 1/19) ?

does 2/20 * 1/19 make 2/380?

then how would i take that from 1
8. (Original post by ihatePE)
so 1 - (2/20 * 1/19) ?

does 2/20 * 1/19 make 2/380?

then how would i take that from 1
Yeah, it does. What's ?
9. (Original post by Zacken)
Yeah, it does. What's ?
189/190?

would i need to simplify?
Spoiler:
Show
im literally so freaked out at how stupid i am right now
10. (Original post by ihatePE)
189/190?

would i need to simplify?
Spoiler:
Show
im literally so freaked out at how stupid i am right now
How could you simplify that?
11. (Original post by Zacken)
How could you simplify that?
i see :P

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: April 10, 2016
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:
Today on TSR

### How does exam reform affect you?

From GCSE to A level, it's all changing

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams