4 (c) Probability (1 Viewer)

sando

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Is it replacing or not replacing ?
 

DeathB4Life

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i assumed it wasnt replacing for the sole reason being that its the first thing that came to my head.

"pick 3 squares" when i hear that i naturally think "3 different squares" but its open to debate.
 

P_Dilemma

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i) What is the probability that Tanya chooses three white squares?

1/32 x 1/31 x 1/30 = 1/29760

ii) what is the probability that Tanya chooses three squares the same colour?

1/29760 x 2 = 1/14880

iii) What is the probability that the squares chosen are NOT the same colour?

1 - 1/14880 = 14879/14880

Hope they're right, or else i'm screwed...

-P_D
 

sando

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umm sorry to tell u, but they are wrong..

half the squares are white.. not only 1 in 32.. lol
 

helz_h

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i had...

i) What is the probability that Tanya chooses three white squares?

32/64 x 31/63 x 30/62 = 5/42

ii) not sure, but i thought it was just 5/42

iii) 1-5/42 = 37/42


I could be wrong though....
 

helz_h

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i had...

i) What is the probability that Tanya chooses three white squares?

32/64 x 31/63 x 30/62 = 5/42

ii) not sure, but i thought it was just 10/42

iii) 1-5/42 = 37/42


I could be wrong though....
 

DeathB4Life

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edit: guy above me correct

i think i put those answers down

*squinted face of recalling
 
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P_Dilemma

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Oh CRAP!!!!!!!

How did i screw up that bad... I must look like an idiot now...

-P_D
 

sando

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shit.. i said replacing.. stupid question

i will lose all 5 marks now ay
 

H.A.L.

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helz_h said:
i had...

i) What is the probability that Tanya chooses three white squares?

32/64 x 31/63 x 30/62 = 5/42

ii) not sure, but i thought it was just 10/42

iii) 1-5/42 = 37/42


I could be wrong though....
Your pretty close.

ii.) 10/42 is correct but can be simplified to 5/21, so lets hope the marker isn't a prick and gives you the mark, as some people are fussy about these things.

iii.) P(Of three square chosen are different colour) = 1 - P(Three squares the same colour)

Therefore: 1 - 5/21 (from part ii.)

= 16/21

That's at least what I put, and I've seen a few others with the same answer.
 

dunno04

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fishy89sg said:
do u get marks for cfpa (correct from previou answer)
hmm...i think they do replace it.
DOn't they?

=.=
 

meg_1_2_3_4_5

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i really really hope it was replacement... the question wasn't really that clear
 

UzurOger

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I did this question twice...1st time not replacing so it was like 32\64 x 31\63 etc

but then i thought its a chess board so you cant loss any squares so i did it again and got an answer like 1\8 for the 1st question which seems like the logical answer meh hope i got it right
 

izaon

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It does say she chooses three "different" squares at random
so i assume that means take out the square u just had
 

da1

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the qn says TANYA CHOOSES THREE DIFFERENT SQUARES AT RANDOM so its without replacement
 

ashh

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i took it that u dont replace it, but it is kinda confusing coz she could pick 1 sqaure, then replace it and pick again. spent a while thinking about it...i think it couldv been worded easier, oh well
 

nickyroony

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UzurOger said:
I did this question twice...1st time not replacing so it was like 32\64 x 31\63 etc

but then i thought its a chess board so you cant loss any squares so i did it again and got an answer like 1\8 for the 1st question which seems like the logical answer meh hope i got it right
Yup! Likewise.
 

acmilan

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H.A.L. said:
Your pretty close.

ii.) 10/42 is correct but can be simplified to 5/21, so lets hope the marker isn't a prick and gives you the mark, as some people are fussy about these things.

iii.) P(Of three square chosen are different colour) = 1 - P(Three squares the same colour)

Therefore: 1 - 5/21 (from part ii.)

= 16/21

That's at least what I put, and I've seen a few others with the same answer.
^^correct

No replacement, otherwise you could pick the same square, which would go against picking different squares.
 

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