Someone help I will give medal
Question involving the rolling of two fair dice.
What is the probability of one of the dice showing 3 or the sum being at least 8?

- Pulsified333

- katieb

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- anonymous

Well do you know how to compute probability?

- Pulsified333

yes I do, I thought the answer was 16/36 but it was wrong

- anonymous

So the probability of rolling 3 is equal on /both/ of them so we just leave that probability as 1/6th, not 1/12th. Does that help?

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- anonymous

Huh? On a fair dice there's a 1 in six chance of rolling a 3.

- Pulsified333

yes but can't you roll a 3 on lets say die 1 or die 2?

- anonymous

Yes, but that's 2/12 chance, which simplifies down to 1/6.

- Pulsified333

oh

- anonymous

Actually, 16/36 can be simplified. Maybe the answer needs to be simplified. What format is the test?

- Pulsified333

it simplifies it for you

- anonymous

Oh. well then.

- anonymous

So we've got 1/6th. Then we need to work out the chance of rolling a sum of of over eight and add it to 1/6th.

- Pulsified333

would it be over 36?

- anonymous

The denominator?

- Pulsified333

yes

- anonymous

IDK XD
I'll work it out.

- anonymous

So how many combinations are there that equal above 8?

- Pulsified333

5

- anonymous

So there is a 5/36 (yeah, it is 36) chance of getting +8. So find a common denominator between 1/6th and 5/36ths and add them together.

- Pulsified333

i made a mistake

- Pulsified333

its the sum of at least 8

- Pulsified333

which equals 15/36

- anonymous

Ok. So still, multiply 'till you've got a common denominator + add them together.

- Pulsified333

quick question

- anonymous

Yeah?

- Pulsified333

wouldn't the probability of getting a 3 on one die be 10/36

- anonymous

I think the probability of 1 showing a 3 is 11/36.
http://www.sms.rcs.k12.tn.us/TEACHERS/flaniganj/TEST/chapter_9_files/i0100000.jpg

- anonymous

Well 36/6 = 6 so it's 6/36

- Pulsified333

where is the 6 coming from?

- Pulsified333

would the answer be 25/36

- anonymous

You can get a 3 six different way on the first die, and 6 different ways on the second die. But two of those is (3, 3) so you subtract 1 to get 11/36 ways.
11/36 + 15/13 = 26/36

- anonymous

* 11/36 + 15/36 = 26/36

- Pulsified333

oh i see

- Pulsified333

the answer is still wrong

- anonymous

Well you're multiplying both sides of the fraction to give it 36 as a denominator, and you need to times 6 by 6 to get to 36, so so you also multiply 1 by six to get from 1/6 to 6/36, which you can add to 15/36.

- anonymous

Which by my admittedly thirteen-year-old brain is 21/36.

- anonymous

did you try the 25/36 you came up with?
I'm guessing they want you to exclude the double roll.

- Pulsified333

yeah probably because it says one 3 not 2

- anonymous

was that it?

- Pulsified333

i didn't try it yet. I only have 2 attempts left

- Pulsified333

do you think 25/36 would be the right answer if its not including the double roll

- anonymous

yeah, not including it, it's 25/36.
including it, it's 26/36 or 13/18.

- Pulsified333

no its not it either

- Pulsified333

;(

- anonymous

red = one 3
blue = sum at least 8|dw:1443039212787:dw|

- anonymous

there are 4 double counts. so they have to be subtracted.
10/36 + 15/36 - 4/36 = 21/36

- anonymous

I think

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