You are Here: Home >< Maths

# Probability Question GCSE Watch

Announcements
1. Hi could someone explain to me how this answer is correct

Q2 If the probability of spinning red on a spinner is 1 – 3x, find the probability of spinning any colour except red.

answer = 3x but I don't understand how

thanks
2. The probability of 1 includes red and every other colour.
So if you do 1-Probability(Red), then the rest of the colours probability can be given.
1-(1-3x) =
1-1= 0
You have a "-" outside the bracket and inside the bracket. Two minuses make a plus. So --3x is 3x.
Hope I was clear enough, please ask more questions if I wasn't clear
3. (Original post by MezmorisedPotato)
The probability of 1 includes red and every other colour.
So if you do 1-Probability(Red), then the rest of the colours probability can be given.
1-(1-3x) =
1-1= 0
You have a "-" outside the bracket and inside the bracket. Two minuses make a plus. So --3x is 3x.
Hope I was clear enough, please ask more questions if I wasn't clear
Still a bit lost if you do 1-(1-3x) and that is the same as 1-1

so does that mean that 1-3x is equal to 1 ?
4. (Original post by samaad1)
Still a bit lost if you do 1-(1-3x) and that is the same as 1-1

so does that mean that 1-3x is equal to 1 ?
Ok so it's like this. When you do 1( which is the total probability of red and all colours) - probability of red, then you get the probability of the rest. You know red has a probability of 1-3x.
So take 1-3x from the total probability which is 1.
1- (1-3x)
1-1 is 0.
Since the 1 has been sorted out, you only have the --3x left which is 3x. You got to work on the bracket in steps

Zacken will probably explain a lot better!!
5. (Original post by MezmorisedPotato)
Ok so it's like this. When you do 1( which is the total probability of red and all colours) - probability of red, then you get the probability of the rest. You know red has a probability of 1-3x.
So take 1-3x from the total probability which is 1.
1- (1-3x)
1-1 is 0.
Since the 1 has been sorted out, you only have the --3x left which is 3x. You got to work on the bracket in steps

Zacken will probably explain a lot better!!
still very confused of how can 1-3x be equal to 1
6. (Original post by samaad1)
Hi could someone explain to me how this answer is correct

Q2 If the probability of spinning red on a spinner is 1 – 3x, find the probability of spinning any colour except red.

answer = 3x but I don't understand how

thanks
Let's say the probability of getting a red is , then the probability of getting a blue is , green is , etc... do the same for every single colour. Now you know that you spinning the spinner means you must land on some colour. So the probability that you get a colour is 1. But that's the same as saying that the sum of the probabilites of getting red, green, blue, etc.. add up to 1.

So . Now, for you not to get a red means that you must get a blue or green or yellow or whatvever. Which is the probability of getting one of every single colour minus the probability of getting a red.

So since the probability of getting any colour is 1, then you subtract the probability of getting a red to get the probability of not getting a red. This is .

In your case, so you do . We are not saying that . We are saying that .
7. (Original post by Zacken)
Let's say the probability of getting a red is , then the probability of getting a blue is , green is , etc... do the same for every single colour. Now you know that you spinning the spinner means you must land on some colour. So the probability that you get a colour is 1. But that's the same as saying that the sum of the probabilites of getting red, green, blue, etc.. add up to 1.

So . Now, for you not to get a red means that you must get a blue or green or yellow or whatvever. Which is the probability of getting one of every single colour minus the probability of getting a red.

So since the probability of getting any colour is 1, then you subtract the probability of getting a red to get the probability of not getting a red. This is .

In your case, so you do . We are not saying that . We are saying that .
thank you I think I fully understand now
8. (Original post by MezmorisedPotato)
Zacken will probably explain a lot better!!
(Original post by samaad1)
thank you I think I fully understand now
No problem, give MezmorisedPotato his fair share of credit as well
9. (Original post by Zacken)
No problem, give MezmorisedPotato his fair share of credit as well
yup I repped him
10. (Original post by samaad1)
yup I repped him
Awesome

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: September 25, 2016
Today on TSR

### Starting your personal statement?

This is how Oxbridge students do it.

### This compliment left me speechless...

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Useful resources

## Make your revision easier

### 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

Can you help? Study help unanswered threads

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.