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The probability of randomly selecting a prime or an even number

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Carcass
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The probability of randomly selecting a prime or an even number [#permalink] New post   11 Oct 2021, 05:18
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Quantity A
Quantity B
The probability of randomly selecting a prime or an even number from the set 1,2,4,7,9
45



A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given.
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B
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eskay1981
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Re: The probability of randomly selecting a prime or an even number [#permalink] New post   11 Oct 2021, 10:02
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Carcass wrote:
Quantity A
Quantity B
The probability of randomly selecting a prime or an even number from the set 1,2,4,,7,9
45



A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given.


Favourable outcomes for A = {2,4,7} - even or prime = 3/5

B is greater
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Re: The probability of randomly selecting a prime or an even number [#permalink] New post   14 Dec 2023, 09:33
Carcass , what is the difference between my approach and approach taken by eskay1981 ?

P(Prime or Even)=P(Prime)+P(Even)−P(Prime and Even)

P(Prime or Even)=2/5 + 2/5 - (2/5 *2/5)

P(Prime or Even)= 16/25
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The probability of randomly selecting a prime or an even number [#permalink] New post   14 Dec 2023, 12:08
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Frankly I do not know what he did

prime are 2/5
even are 2/5

Toral 4/5

Minus

the number/s that are prime and even at the same time which is only 2 . so we have 1/5

4/5-1/5=3/5

B is greater than A

OR we can also say the following

number of primes OR even numbers in the set/number of elements in the set. our numerator is the sum of primes and even purged by the overlap which is the 2
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Re: The probability of randomly selecting a prime or an even number [#permalink] New post   15 Dec 2023, 06:04
Carcass sir , can you please tell my approach is correct or not ?
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Re: The probability of randomly selecting a prime or an even number [#permalink] New post   15 Dec 2023, 07:58
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You approach is correct but I not get the part 2/5* 2/5

Posted from my mobile device
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Re: The probability of randomly selecting a prime or an even number [#permalink] New post   15 Dec 2023, 19:36
Carcass sir, it denotes overlapping between prime and even outcomes.
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Re: The probability of randomly selecting a prime or an even number [#permalink] New post   15 Dec 2023, 23:43
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Until there I understand but why 2/5*2/5?

The overlap is just the number that at the same time is prime and even which is 2
or a number over 5

1/5

4/5-1/5=3/5
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Re: The probability of randomly selecting a prime or an even number [#permalink] New post   25 Dec 2023, 08:18
in the question it says even or a prime number. when it is specified either this or that. so 2/5*2/5 is wrong here. Both even and prime cases are supposed to be taken together. Hence, 2,4,7 = 3/5
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Re: The probability of randomly selecting a prime or an even number [#permalink]
25 Dec 2023, 08:18
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