You are Here: Home >< Maths

# Find probability that number of 2.4<T<2.6 is at least 15 watch

1. Table cloths made with normal distribution
T ~ N(2.5 , 0.1298^2)
Table cloth can be sold if 2.4<T<2.6. A sample of 20 table cloths is taken, how many can be sold?
________

I know P(2.4<T<2.6) = 0.5589
So the expected number of table cloths is 11.178.
But how do I find the probability that it is greater?
2. (Original post by Retsek)
Table cloths made with normal distribution
T ~ N(2.5 , 0.1298^2)
Table cloth can be sold if 2.4<T<2.6. A sample of 20 table cloths is taken, how many can be sold?
________

I know P(2.4<T<2.6) = 0.5589
So the expected number of table cloths is 11.178.
But how do I find the probability that it is greater?
Given that each table cloth is subject to a pass/fail test and that there is a known number of tests, you could explore the probability that a particular number, or range of numbers, of table cloths can be sold by looking at the binomial distribution B(20, 0.5589).
3. Probability that what is greater? If you probability is correct then 11.178 is right, you dont need to do anything else beside giving it to the nearest whole number.
Probability that what is greater? If you probability is correct then 11.178 is right, you dont need to do anything else beside giving it to the nearest whole number.
Probability that out of the 20, 15 or more are of a suitable width.
5. (Original post by old_engineer)
Given that each table cloth is subject to a pass/fail test and that there is a known number of tests, you could explore the probability that a particular number, or range of numbers, of table cloths can be sold by looking at the binomial distribution B(20, 0.5589).
Brilliant fab!
6. (Original post by Retsek)
Probability that out of the 20, 15 or more are of a suitable width.
If that is part of the question, you didnt write it in your initial post. Nonetheless, are you familiar with the binomial distribution?
If that is part of the question, you didnt write it in your initial post. Nonetheless, are you familiar with the binomial distribution?
My bad you're right I should've proof-read before posting, yeah I think I know how to do it now:
T ~ B(20 , 0.5589)
P(T>=15)
1 - P(T=<14)
1 - 0.9352 = 0.0648

Is my value for P(T=<14) correct? I'm not sure I put it in my calculator properly
8. (Original post by Retsek)
My bad you're right I should've proof-read before posting, yeah I think I know how to do it now:
T ~ B(20 , 0.5589)
P(T>=15)
1 - P(T=<14)
1 - 0.9352 = 0.0648

Is my value for P(T=<14) correct? I'm not sure I put it in my calculator properly
How did you find a cumulative probabilty using the calculator? To find P(X>=15) you have to add up the separate prbabilites from 15 to 20.
9. (Original post by Retsek)
My bad you're right I should've proof-read before posting, yeah I think I know how to do it now:
T ~ B(20 , 0.5589)
P(T>=15)
1 - P(T=<14)
1 - 0.9352 = 0.0648

Is my value for P(T=<14) correct? I'm not sure I put it in my calculator properly
Looks good to me.
How did you find a cumulative probabilty using the calculator? To find P(X>=15) you have to add up the separate prbabilites from 15 to 20.
I've got a fancy calculator that can do distributions and stuff, put in:
x = 14
N = 20
p = 0.5589
To get P(X=<14)
11. (Original post by Retsek)
I've got a fancy calculator that can do distributions and stuff, put in:
x = 14
N = 20
p = 0.5589
To get P(X=<14)
Nice, is it the fx9860gii by any chance?
Nice, is it the fx9860gii by any chance?
Nope, it's a Casio fx-991EX classwiz
Just the one I was told to get for my further maths a-level ¯\_(ツ)_/¯
13. (Original post by Retsek)
Nope, it's a Casio fx-991EX classwiz
Just the one I was told to get for my further maths a-level ¯\_(ツ)_/¯
(Original post by Retsek)
Nope, it's a Casio fx-991EX classwiz
Just the one I was told to get for my further maths a-level ¯\_(ツ)_/¯
Same feel sorry when I see also those tables in back of textbook / remembering writing out binomial probabilities.
14. (Original post by Canary84)
Same feel sorry when I see also those tables in back of textbook / remembering writing out binomial probabilities.
Is that calculator allowed in the exam?
15. (Original post by dhruvap)
Is that calculator allowed in the exam?
Yeah it's the one recommended to us by the exam board and is sold in our maths department no need to worry 😅

### 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: March 7, 2018
Today on TSR

### Results day under a month away

How are you feeling?

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