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This question doesn't work now on account of gay marriage. It requires 30/45 of the females to be married to 30/80 of the males.

2/3·1/80=1/120
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Male =80 & female= 45

married couple = 30
so
married males; 30 and females 30

we can say
P of married males ; 30/80
and them with females ; 1/45
30/80 * 1/45
IMO 1/120 ; D
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sg20
In a party there were 80 males and 45 females. One pair of a male and a female was selected at random for dance, what is the probability that a pair selected is a married couple if there were total 30 married couples in the party?

a) 1/30
b) 1/3600
c) 1/1200
d) 1/120
e) none of these

Doesn't look like a 700 question tbh.
You need to pick one couple from the 30 married, which can be done in 30C1 ways. Let's get to the denominator, you need to form a *straight* couple, that means you need to pick 1 from the males and 1 from the females to qualify as a couple. This can be done in 80C1*45C1 ways.

So IMO the probability will be 30/80*45 = 1/120.

Posted from my mobile device
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Bunuel VeritasKarishma

When they ask for the probability of selecting a couple, why can't we do 60C1 x 2 in the numerator? (60 ways of selecting the first person and then since the person can be either male or female - 2 ways of selecting the first person). If not in this question, can you also please elaborate when can we use this technique.
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crackGMAT760
Bunuel VeritasKarishma

When they ask for the probability of selecting a couple, why can't we do 60C1 x 2 in the numerator?

crackGMAT760

60C1*2 = 120

While there are only 30 ways of choosing a couple out of 30 couples.

therefore 60C1*2 doesn't have merit.

To. make it slightly correct

60C1 = Number of ways of choosing one person out of 30 couples (60 individuals)

But now, the second person can be chosen in ONLY 1 WAY because chosen person has only 1 partner who makes couple with chosen one.

so you don't need to multiply it by 2

in that case the method will be 60C1*1/(80*45*2)

Denominator also must include arrangement if Numerator includes that (60C1 includes arrangement)

I hope this help! :)
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sg20
In a party there were 80 males and 45 females. One pair of a male and a female was selected at random for dance, what is the probability that a pair selected is a married couple if there were total 30 married couples in the party?

a) 1/30
b) 1/3600
c) 1/1200
d) 1/120
e) none of these

Chances of selecting a married couple = 30
Chances of selecting a male = 80
Chances of selecting a female = 45


Hence, probability = 30/(80*45) = 1/120

OA: D
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