Probability Q

[Mstoothlady2012]

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Two numbers between 1 and 30 inclusive are drawn in a contest. What is the probability that both numbers are even?

I dont know when to use what among these 3 choices...

just use straight up 2/15 <-- since we have 15/30 even numbers and we are picking 2 numbers

or use (15/30)(15/30)<-- coz they both are independent of each other so you have 1/2 probability of picking an even number every time!

or use (15/30)(14/29) <-- coz when you take out 1 even number, you have 1 less even number hence 1 less total numbers.

confuses the hell out of me!!! 😡 These are simple probabilities I should not be loosing points in these.....can some1 break it down for me plz? Thanks!

 

[Mstoothlady2012]

no1 can help me out? 🙁

 

[Glycogen]

Mstoothy,are you sure that 1 nad 30 are included or not.I remember that I had a similar Q before and it said that we have to consider total of 28 numbers b/c it says between 1 and 30,which means 1 and 30 are excluded!

 

[Mstoothlady2012]

Mstoothy,are you sure that 1 nad 30 are included or not.I remember that I had a similar Q before and it said that we have to consider total of 28 numbers b/c it says between 1 and 30,which means 1 and 30 are excluded!

it says 1 and 30 inclusive in the question

 

[Optimism Smiles]

Mstoothy,are you sure that 1 nad 30 are included or not.I remember that I had a similar Q before and it said that we have to consider total of 28 numbers b/c it says between 1 and 30,which means 1 and 30 are excluded!

haha I was wondering that myself, but I just looked it up on wiki and it said that "inclusive" means that the set starts with 1 and ends with 30.

 

[HoangDDS]

Hey ms.toothy.

If you put the even number back after you pulled out. Then i would do:
15/30 * 15/30 = .25

If you dont put it back then:
15/30 * 14/29 = >.25 but very close. I think its about 0.23.

But I'm actually I should be one of the last person to respond, since my QR is just horrible. But just thought I try to help you if I can.

What's the real answer?

 

[Mstoothlady2012]

Hey ms.toothy.

If you put the even number back after you pulled out. Then i would do:
15/30 * 15/30 = .25

If you dont put it back then:
15/30 * 14/29 = >.25 but very close. I think its about 0.23.

But I'm actually I should be one of the last person to respond, since my QR is just horrible. But just thought I try to help you if I can.

What's the real answer?

This question is from destroyer and the answer shown is (15/30)(15/30) = 1/4 = 0.25

In this case it wouldnt make a huge difference if we do that or (15/30)(14/29), but there are problems where it makes difference. And it makes me so mad that every question has its own little solution. Well the question is also vague b/c it doesnt say if we are putting that # back in or not. I would hate to loose points on these easy probability question, b/c I sure can't do those hard ones!! oh well, Thanks for your help!

 

[HoangDDS]

This question is from destroyer and the answer shown is (15/30)(15/30) = 1/4 = 0.25

In this case it wouldnt make a huge difference if we do that or (15/30)(14/29), but there are problems where it makes difference. And it makes me so mad that every question has its own little solution. Well the question is also vague b/c it doesnt say if we are putting that # back in or not. I would hate to loose points on these easy probability question, b/c I sure can't do those hard ones!! oh well, Thanks for your help!

DITTO. I think QR is the toughest section for me on this exam. Good luck on the rest.

 

[TheGreenWave]

This question is from destroyer and the answer shown is (15/30)(15/30) = 1/4 = 0.25

In this case it wouldnt make a huge difference if we do that or (15/30)(14/29), but there are problems where it makes difference. And it makes me so mad that every question has its own little solution. Well the question is also vague b/c it doesnt say if we are putting that # back in or not. I would hate to loose points on these easy probability question, b/c I sure can't do those hard ones!! oh well, Thanks for your help!

Ok, I see why youre upset, let me see if I can help. Inclusive and Exclusive tell you whether or not you include the numbers at the front or end of the parameters. Since this is inclusive you include both the 1 and 30, if it was exclusive you would have only numbers 2-29.

As for whether or not the drawn number is put back in, you should look for "with replacement" or "without replacement." If it doesnt say either I would assume w/o replacement. Such is the case here. I believe you must assume w/o replacement and multiply (15/30)(14/29).

IMO destroyer slipped up by not including "with replacement."

 

[Mstoothlady2012]

Ok, I see why youre upset, let me see if I can help. Inclusive and Exclusive tell you whether or not you include the numbers at the front or end of the parameters. Since this is inclusive you include both the 1 and 30, if it was exclusive you would have only numbers 2-29.

As for whether or not the drawn number is put back in, you should look for "with replacement" or "without replacement." If it doesnt say either I would assume w/o replacement. Such is the case here. I believe you must assume w/o replacement and multiply (15/30)(14/29).

IMO destroyer slipped up by not including "with replacement."

yeaa that makes sense! so when is that you can use 2/15...can you give me an example plz?

 

[TheGreenWave]

yeaa that makes sense! so when is that you can use 2/15...can you give me an example plz?

Sorry Mstoothlady, I spent a few mins trying to think of a situation where you would get 2/15, but came up blank. In the problem described above you would never use logic to get 2/15. Obviously if the problem was different that could potentially be the answer... If you find one where that is the solution i could maybe walk you through it

Now I gotta get back to some more Bio Review... last day of studying before saturday!!

 

[klutzy1987]

This exact question was asked and explained in detail like 2 days ago. Look at the old thread and you should understand what you needed to know.

 

[Mstoothlady2012]

Sorry Mstoothlady, I spent a few mins trying to think of a situation where you would get 2/15, but came up blank. In the problem described above you would never use logic to get 2/15. Obviously if the problem was different that could potentially be the answer... If you find one where that is the solution i could maybe walk you through it

Now I gotta get back to some more Bio Review... last day of studying before saturday!!

Big day on saturday huh? me 2...just can't get enuff of bio lol

 

[HoangDDS]

yeaa that makes sense! so when is that you can use 2/15...can you give me an example plz?

You can use 2/15 when each event can occur with the same probability of yo1/15. Let say you have a roulette wheel with #s 1-15. And asked what are the chances of you getting a 1 or a 2.

So each slot has an even chance of occurring and reoccurring --- 1/15 . So the chance of you hitting 1 is 1/15, and the chance of you hitting 2 is 1/15.

Then you just combined them 1/15 + 1/15 = 2/15 chances of landing on 1 or 2.

 

[Mstoothlady2012]

You can use 2/15 when each event can occur with the same probability of yo1/15. Let say you have a roulette wheel with #s 1-15. And asked what are the chances of you getting a 1 or a 2.

So each slot has an even chance of occurring and reoccurring --- 1/15 . So the chance of you hitting 1 is 1/15, and the chance of you hitting 2 is 1/15.

Then you just combined them 1/15 + 1/15 = 2/15 chances of landing on 1 or 2.

yes makes sense!!

Who says you are bad at QR? 😛

 

[TheGreenWave]

Big day on saturday huh? me 2...just can't get enuff of bio lol

LoL, enough Bio is never enough, ya know?? I made reviews for gen chem, orgo, and bio. My chem ones combine to 8pgs, my bio one is 17!!

Good Luck on the 19th, you will rock 👍

 

[Mstoothlady2012]

LoL, enough Bio is never enough, ya know?? I made reviews for gen chem, orgo, and bio. My chem ones combine to 8pgs, my bio one is 17!!

Good Luck on the 19th, you will rock 👍

Thanks! hope so...GL to you too!!!