username2803872
Badges: 12
Rep:
?
#1
Report Thread starter 4 years ago
#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
0
reply
MezmorisedPotato
Badges: 18
Rep:
?
#2
Report 4 years ago
#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.
Therefore your answer is 3x
Hope I was clear enough, please ask more questions if I wasn't clear
0
reply
username2803872
Badges: 12
Rep:
?
#3
Report Thread starter 4 years ago
#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.
Therefore your answer 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 ?
0
reply
MezmorisedPotato
Badges: 18
Rep:
?
#4
Report 4 years ago
#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!!
1
reply
username2803872
Badges: 12
Rep:
?
#5
Report Thread starter 4 years ago
#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
0
reply
Zacken
Badges: 22
Rep:
?
#6
Report 4 years ago
#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 r, then the probability of getting a blue is b, green is g, 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 r + b + g + \cdots  = 1. 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 1 - r.

In your case, r = 1-3x so you do 1 - (1-3x) = \underbrace{1 - 1}_{=0} -- 3x = 3x. We are not saying that 1 - 3x = 1. We are saying that 1 - (1-3x) = 3x.
1
reply
username2803872
Badges: 12
Rep:
?
#7
Report Thread starter 4 years ago
#7
(Original post by Zacken)
Let's say the probability of getting a red is r, then the probability of getting a blue is b, green is g, 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 r + b + g + \cdots  = 1. 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 1 - r.

In your case, r = 1-3x so you do 1 - (1-3x) = \underbrace{1 - 1}_{=0} -- 3x = 3x. We are not saying that 1 - 3x = 1. We are saying that 1 - (1-3x) = 3x.
thank you I think I fully understand now
0
reply
Zacken
Badges: 22
Rep:
?
#8
Report 4 years ago
#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
1
reply
username2803872
Badges: 12
Rep:
?
#9
Report Thread starter 4 years ago
#9
(Original post by Zacken)
No problem, give MezmorisedPotato his fair share of credit as well
yup I repped him
0
reply
Zacken
Badges: 22
Rep:
?
#10
Report 4 years ago
#10
(Original post by samaad1)
yup I repped him
Awesome
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

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.

Personalise

How would you feel if uni students needed to be double vaccinated to start in Autumn?

I'd feel reassured about my own health (20)
17.39%
I'd feel reassured my learning may be less disrupted by isolations/lockdowns (35)
30.43%
I'd feel less anxious about being around large groups (12)
10.43%
I don't mind if others are vaccinated or not (13)
11.3%
I'm concerned it may disadvantage some students (5)
4.35%
I think it's an unfair expectation (28)
24.35%
Something else (tell us in the thread) (2)
1.74%

Watched Threads

View All
Latest
My Feed