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# binomial distribution help needed watch

1. Can someone explain why they said that p(x>15)=p(y<or equal to 4) its the last line on the workout example. part a
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2. (Original post by assassinbunny123)
Can someone explain why they said that p(x>15)=p(y<or equal to 4) its the last line on the workout example. part a
Because having more than 15 customers buy the tea is the same as having less than or equal to 4 customer NOT buying the tea.

Reverse the logical statement.
3. (Original post by assassinbunny123)
Can someone explain why they said that p(x>15)=p(y<or equal to 4) its the last line on the workout example. part a
There are two ways to work out the answer. Either by considering the prob of buying tea =0.7 or by looking at fewer than 5 not buying tea. I think most people would go for the first approach but they are just saying there is another way.
4. (Original post by Muttley79)
There are two ways to work out the answer. Either by considering the prob of buying tea =0.7 or by looking at fewer than 5 not buying tea. I think most people would go for the first approach but they are just saying there is another way.
I don't know too much about old spec stats but wouldn't you have to use the Y random variable since the probabilities in the table are < 0.5?

In the new spec you'd just use your calculator with p = 0.7.
5. (Original post by Notnek)
I don't know too much about old spec stats but wouldn't you have to use the Y random variable since the probabilities in the table are < 0.5?

In the new spec you'd just use your calculator with p = 0.7.
I did not know whether OP is old or new spec.
6. (Original post by Muttley79)
I did not know whether OP is old or new spec.
I think it's an old spec textbook but the OP could be using it for new spec.
7. (Original post by Notnek)
I think it's an old spec textbook but the OP could be using it for new spec.
Lots of schools are using the old books.
8. (Original post by Muttley79)
Lots of schools are using the old books.
Yes they are which is a shame, especially for stats.
9. (Original post by Notnek)
Yes they are which is a shame, especially for stats.
I agree...
10. (Original post by Notnek)
I don't know too much about old spec stats but wouldn't you have to use the Y random variable since the probabilities in the table are < 0.5?

In the new spec you'd just use your calculator with p = 0.7.
old spec but how would you do this question on a calculator since i find going to the tables a bit tedious
11. (Original post by assassinbunny123)
old spec but how would you do this question on a calculator since i find going to the tables a bit tedious
Probability for a binomial distribution is . So for you simply add up all the 'equality probabilities' , which can be denoted by .

In your question, you are looking for from which can be found from the calculator by typing in

If you calculator doesnt have a sum button, then you'd need to sum these probabilities individually, which as you might expect is tedious as well if you're summing up many of them - hence the table in the formula booklet.
12. (Original post by assassinbunny123)
old spec but how would you do this question on a calculator since i find going to the tables a bit tedious
You’re on old spec so probably don’t have a binomial distribution function in your calculator. You could sum the probabilities but it’s a waste of time.

A lot of questions will assume you’re using tables so it’s best to stick to tables for old spec even if your calculator does have the function.

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