Competition - post a photo you've taken of nature >>

AQA A2 Mathematics MS2B Statistics 2B - 21st June 2016

Scroll to see replies

Reply 200

irMike

Original post by tanyapotter

was it just 0.35x0.45 for that one question?

That sounds familiar

Reply 201

sam_97

Unofficial mark scheme on first page :smile:

Reply 202

irMike

Original post by Sam1231

I think its because it must be open ended , and there is likelly to be peak times

Ah, I think I put that it's not random, because different customers are likely to take out different numbers of books, e.g. because of different ages/preferences. And don't even remember my second point, something to do with it not being a constant average rate because they can only take out six books I think

Reply 203

Ayeros

Original post by tanyapotter

was it just 0.35x0.45 for that one question?

That's what I had put but other people did 2(0.35x0.45) which I guess makes sense?

Reply 204

irMike

Original post by Ayeros

That's what I had put but other people did 2(0.35x0.45) which I guess makes sense?

Ah yeah that's what I did, there were two ways of doing it so had to be doubled, Either customer could have been the one to purchase >3 or <3

Reply 205

tanyapotter

Original post by Ayeros

That's what I had put but other people did 2(0.35x0.45) which I guess makes sense?

i'm fairly sure it's just 0.45x0.35. They're just two independent events so I think we're correct.

Reply 206

Ayeros

Original post by tanyapotter

i'm fairly sure it's just 0.45x0.35. They're just two independent events so I think we're correct.

Yeah that's what I thought too, one of my friends did 2(0.45x0.35) and said it was because of the 2 possible combinations but his explanation didn't really make much sense.

Reply 207

sam_97

Original post by tanyapotter

i'm fairly sure it's just 0.45x0.35. They're just two independent events so I think we're correct.

Original post by Ayeros

Yeah that's what I thought too, one of my friends did 2(0.45x0.35) and said it was because of the 2 possible combinations but his explanation didn't really make much sense.

You have to multiply (0.35 x 0.45) by 2 (2!). I'll try and briefly explain why this is below.

If you have two people A and B borrowing books from the library, person A could borrow less than 3 books whereas person B might borrow more than three. The probability of this happening is 0.35 x 0.45 = 0.1575.

However, what if person A borrowed more than 3 books and person B borrowed less than 3 instead? The probability of this happening would again be 0.1575.

Since there are two possible combinations, the answer to the question is 2 x 0.1575 = 0.315.

(edited 7 years ago)

Reply 208

Sam1231

No you have to times it by 2! Which is just 2, because it could be .... The first person could have picked less then three , then the next more than three , or the first more than three and the second less than three . If you do it using a probabillity tree you can see it a bit clearer

Reply 209

Hjyu1

If I dropped 15-20 marks what do you think that could be

Reply 210

sam_97

Original post by Sam1231

Yeah 2! is correct. If there were three people for example you would have 3! = 6 different combinations

Reply 211

tanyapotter

Original post by sam_97

that makes sense!

Reply 212

Jm098

for the diesel question couldn't you just say it doesn't matter what engine she chooses as we have just accepted the null?

Reply 213

Hjyu1

Original post by Jm098

for the diesel question couldn't you just say it doesn't matter what engine she chooses as we have just accepted the null?

I said that might be a variety of answers (but I think I'm going to struggle to get a B made so many stupid errors )

Reply 214

-jordan-

For 6bii would it be acceptable to say the calculated mean was above Island B's confidence interval? Therefore it suggests it cant be shorter than on the mainland.

Reply 215

Jm098

can anyone remember the means for the poisson?

Reply 216

ruishiZ

how many marks will I lose if I forgot to use the yate's correction? will the result in part a affect my mark in part b which asks for comments?

Reply 217

sam_97

Original post by Jm098

can anyone remember the means for the poisson?

Volvox aureus - 4.5
Volvox globator - 2.3
Volvox tertius - 1.2

Reply 218

sam_97

Original post by -jordan-

For 6bii would it be acceptable to say the calculated mean was above Island B's confidence interval? Therefore it suggests it cant be shorter than on the mainland.