Probability Question (1 Viewer)

[~ ReNcH ~]

will u get a carried error if u put 5/72 as i added 36+36 instead of 36*36

Depends on the criteria.
If the criteria state that you need the right answer to get full marks, you'll probably only get 1/2. If marks are given only for your method, and provided you clearly show what method you have used to solve the problem, you may still get full marks.

 

[JayWalker]

Not sure if anyone has said this yet but I think the answer is:

1 - P(Sum isn't less than 45)
=
1 - (1/36 * 1/36)
=
1 - 1/1296
= 1295/1296

Lol Acid,

What about rolling a 5,5 = 25, and then a 4,5 = 20
.... let alone a few more... therefore, your incorrect...

You've only taken into consideration a 25 + 25 = 50..

I also did a 1 - P( )

Well, not everyone is good at maths

Mizz: There are 5 ways greater than 45

Please show us, share your wisdom? how do you get 46, 47, 48, 49 ? Let us know

 

[simon_hitchcock]

ok i must really suck but my answer was 7/9

 

[Mushy18]

hmmm......i got 8/9.
P(x) = 1 - P(more than or equal to 45)
= 1 - ( 4*5 + 5*5 ) + (5*5 + 5*5)
= 8/9

 

[O-B-1 Ken-O-B]

Mmmm... I haven't answered this question correctly during the exam so there goes another 1 - 2 marks down the drain (an addition to 3 + 1 + 1 + 1 = 6 marks already lost)...

For part (iii), when I did the question again at home, I actually got 143/144 as my answer;

Possible combos for the sum of 45+: (20,25), (20,25), (25,25), (25,20), (25,20)
Therefore there are 5 possible combinations...
Note that there is a probabilty of 2/36 in getting a 20 in any turn.
P(20,25) = 4.(2/36).(1/36) since there are only 4 combinations of (20,25)
P(25,25) = (1/36)^2 since there is only one combo
Therefore P(>=45) = 4.(2/36).(1/36) + (1/36)^2
= 1/144
Therefore P(<45) = 1 - P(>=45)
= 1 - 1/144
= 143/144

I wish I did that in my exam... I'm so kicking myself right now... *Knees himself on his nose... Or get pwned by Greed just like in my avatar...*

 

[garry]

hmmm......i got 8/9.
P(x) = 1 - P(more than or equal to 45)
= 1 - ( 4*5 + 5*5 ) + (5*5 + 5*5)
= 8/9

you left out (5*4+5*5) i guess, i got that 43?/43? which i checked it should be wrong. i guess the correct way to do this question is to think of the combination that can get more equal or more than 45 which is 20,25 and 25,25 (or is it 25,20 should be included?) then find the probability to get each of this combination and 1-ans is the correct result.

 

[chriscity1]

I got like something over thirty six! Aaaahhhh! And I thought I was doing soo well.

 

[xeriphic]

let me see...should be

P(<45) = 1 - [ (1/36 *1/36) + (1/36 * 2/36*) + (2/36 * 1/36) ]

think tat's how i wrote it...

yups this is the way, you had to draw up the table of total sum

 

[idontgetit]

Therefore P(<45) = 1 - P(>=45)
= 1 - 1/144
= 143/144

I wish I did that in my exam... I'm so kicking myself right now... *Knees himself on his nose... Or get pwned by Greed just like in my avatar...*

This is what I got. I can't work out wtf the answer is 1291/1296. I mean, it should just be
1 - P(25 + 25) - P(25 + 20) - P (20 +25) = 1 - (1/36)x(1/36) - (2/36)x(2/36)x2
What's wrong with that???

 

[acmilan]

This is what I got. I can't work out wtf the answer is 1291/1296. I mean, it should just be
1 - P(25 + 25) - P(25 + 20) - P (20 +25) = 1 - (1/36)x(1/36) - (2/36)x(2/36)x2
What's wrong with that???

So you are saying the probability of getting a 25 is 2/36? If you use the probability of getting a 25 as 1/36 you will get the answer of 1291/1296. I thought it was 1/36 since the only way to get 25 is to roll two fives which means (1/6)*(1/6) = 1/36

 

[JayWalker]

So you are saying the probability of getting a 25 is 2/36? If you use the probability of getting a 25 as 1/36 you will get the answer of 1291/1296. I thought it was 1/36 since the only way to get 25 is to roll two fives which means (1/6)*(1/6) = 1/36

"So you are saying the probability of getting a 25 is 2/36"
That is incorrect yes..

The Probability of getting a 5 on both die is only 1/36 as you can look at it this way:
Probability(5 on 1st Die) = 1/6
Probability(5 on 2nd Die) = 1/6
Therefore P(25) = 1/36

You cannot consider this twice - i.e you cant say 2 x this as the 5 shows up on the same die anyway, therefore it is only counted once..
Not really sure how to explain this properly but you just cant.. (a 5 shows up on the first die whethers its a 5,5 or a 5,5 [using your thinking])

Bleh who cares

 

[Sweet_Lemon]

umm...stilll discuzz the answer??? faint~~

 

[JayWalker]

umm...stilll discuzz the answer??? faint~~

What are you trying to say?

The Answer is Here:
[>_ is greater or equal to]
P(<45) = 1 - P(>_45)
= 1 -[ P(Getting a 45) + P(Getting a 46) + ... +P(Getting a 50)
It is impossible to get a sum of 46, 47, 48 and 49,
HENCE
= 1 - [(5,5 + 4,5) + (5,5 + 5,4) + (5,5 + 5,5)
= 1 - [1/16 + 1/16 + 1/16]
= 1 - [3/16]
= 13/16
That is the answer that I got and my tutor agrees.. Dunno could be wrong.. general concensus on this board if that 1029 something answer...

::SHRUG::

 

[Sweet_Lemon]

let me see..how can i get this stoopid picture on~~ wait a second~~

 

[bevstarrunner]

The answer is DEFINITELY, CONCLUSIVELY, 100% 1291/1296

 

[bevstarrunner]

What are you trying to say?

The Answer is Here:
[>_ is greater or equal to]
P(<45) = 1 - P(>_45)
= 1 -[ P(Getting a 45) + P(Getting a 46) + ... +P(Getting a 50)
It is impossible to get a sum of 46, 47, 48 and 49,
HENCE
= 1 - [(5,5 + 4,5) + (5,5 + 5,4) + (5,5 + 5,5)
= 1 - [1/16 + 1/16 + 1/16]
= 1 - [3/16]
= 13/16
That is the answer that I got and my tutor agrees.. Dunno could be wrong.. general concensus on this board if that 1029 something answer...

::SHRUG::

you forgot (4,5 + 5,5) and (5,4 + 5,5)

 

[JayWalker]

ow,, yeah !!

Well that makes ME look stupid
That would make....

1 - 5/16
= 11/16..

hows that 1291/1296?

 

[acmilan]

What are you trying to say?

The Answer is Here:
[>_ is greater or equal to]
P(<45) = 1 - P(>_45)
= 1 -[ P(Getting a 45) + P(Getting a 46) + ... +P(Getting a 50)
It is impossible to get a sum of 46, 47, 48 and 49,
HENCE
= 1 - [(5,5 + 4,5) + (5,5 + 5,4) + (5,5 + 5,5)
= 1 - [1/16 + 1/16 + 1/16]
= 1 - [3/16]
= 13/16
That is the answer that I got and my tutor agrees.. Dunno could be wrong.. general concensus on this board if that 1029 something answer...

::SHRUG::

The method i used was


P = 1 - [P(20,25) + P(25,20) + P(25,25)]
= 1 - [(1/36*2/36) + (1/36*2/36) + (1/36*1/36)]
= 1 - [5/1296]
= 1291/1296

The main difference is where you had addition i had multiplication

 

[Sweet_Lemon]

ekekekekekk

 

[acmilan]

I think we should just wait until Jeff Geha writes the answers because we will never have general agreement on this question