HELPPPPPPP

[Crazed Rabbit]

I believe the thing is that she eats 80% of her calories - 800, or 16 chocolates - before she tastes a rum one.

CR

[a completely inoffensive name]

From my poor understanding, I believe CR is right. In a more formal way the answer should be the product of ((n-5)/n) where n=number of chocolates from 30 to 14.

[Fragony]

Make one of these https://upload.wikimedia.org/wikiped...o_binomial.png and a zero equation, set axis on 0.8 et presto

[Husar]

Well, since she won't put any of them back into the box after eating them, it should be a Hypergeometric distribution.

You can replace it with a Binomial distribution if n/N is > 0.05 but I don't think it's the case here.

So you could set:

N = 30
m = 5
n = 16

And set k = 0, which would get you the chance that if she picks 16 chocolates from 30 (5 of which have rum), there will be 0 with rum among the 16 she picked.

It doesn't say anything about whether she will eat one with rum directly afterwards but neither does the task description IMO.

The important part here being that she doesn't put any of the chocolates back and the Hypergeometric distribution is the only discrete distribution we learned that works when you don't put back what you picked out of N.

Edit: Thinking about it again, CR may be right that it implies the 17th will be a rum chocolate nugget, in that case you will have to do it manually I guess. There may be a chance that you could use the geometric distribution as well because N is 30 or so but that seems a bit flaky/inaccurate because it assumes she puts them back after eating them.

Or you could calculate the chance that she eats 16 non-rum nuggets and then calculate the chance that when she picks 1 from the remaining 14 nuggets, it's a rum nugget, then combine the two. Which is how CR did it except you'd speed up the calculation for the first 16 a bit by using the Hypergeometric distribution I guess.

[Centurion1]

wait should i multiply it out or should i use the hypergeometric process. also with the hypergeometric..... confused that k=0 because then it means that you get 5/0 which is undefined.

the point of the question... it is not a trick question in any way its number one for gods sakes and this professor is not going to give us trick questions. All she wants to know is th probability that you will not choose a rum flavored candy by the time she eats 80% of her calories which is 16 candies worth.

so just forget the 17th its irrelevant

[Crazed Rabbit]

My earlier method or the hypergeometric method give the same result. The equation I used was this;


Excel has a function for binomial coefficients - "Combin(top number, bottom number)"

It works thusly;


Yay factorials.

For the hypergeometric, k is the number of successes, n is the number of draws, N is the initial pool, and m is the initial number of what you're trying to pick out.

Remember that for this we're looking at picking 16 other chocolates in a row. So we want to consider picking the other chocolates as a success. Also, even with the hypergeometric equation it's a two part problem - the equation can't give you the answer for picking 16 others in a row and then picking a rum flavored chocolate.

CR

[Centurion1]

right we havent been using excel so its all sort of blurry.

wheni try to do the factorial i get massive unworkable numbers.


and so your saying that k=16; not zero?


the seventeenth candy is absolutely irrelevant. all they want to know is what the probability of NOT selecting a rum candy by the sixteenth

[Centurion1]

Never mind i figured it out. I reached the 1.4% using both methods, i.e. the hypergeometric and the multiplying out manually.

I appreciate the help. Unfortunately I have more to go and other problems i have found issue with.....

Does anyone have any idea on this one?


2. Photocards-R’-Us is a photo card printer. For this year, they have found that 10% of the cards they make are of inferior quality (blurred picture, faded colors, etc.) To attract customers to have their holiday cards printed with them, they are offering a 50% discount to customers who order a box of 50 cards if 10 of the cards in the box are of inferior quality. Manny is going to order a box of 50 Christmas photo cards at Photocards-R’-Us. What is the probability that he will receive a 50% discount on his holiday cards? [10 pts.]


Personally, I thought that it would be like Bayes' but the wording confuses me as well as the application required.

[Husar]

My earlier method or the hypergeometric method give the same result. The equation I used was this;

My dear CR, that is the formula used with the Hypergeometric method.
The hypergeometric method is just a shorter way of doing what you did, I didn't want to sound like what you posted at first was wrong.

confused that k=0 because then it means that you get 5/0 which is undefined.

Then you're doing the binomial coefficients wrong, there shouldn't be a 5/0.

All she wants to know is th probability that you will not choose a rum flavored candy by the time she eats 80% of her calories which is 16 candies worth.

so just forget the 17th its irrelevant

Then just use the hypergeometric method.

right we havent been using excel so its all sort of blurry.

wheni try to do the factorial i get massive unworkable numbers.

On your calculator, to calculate a binomial coefficient (one number above another in parentheses) you can type the upper number, then "nCr" and then the lower number, at least on most calculators I've seen.
No need to work with factorials then.

As for the Hypergeometric method, I thought the wikipedia page would explain that, but:

N = the total number of elements to choose from (30 here)
m = the number of elements in N that have whatever you are looking for (in this case the chocolates with rum = 5)
n = the amount of elements you select (in this case you want the first 16, so you select 16)
k = the number of elements with the attribute you're looking for that end up in n (here you want no rum chocolates in n, thus 0)

Excel is usually nice to use but since all we're usually allowed to use in exams are a pen and a calculator, I wouldn't rely on it if it's the same for you. Not yet anyway.