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Re: At Rocket Brown Elementary School there are 150 students and three [#permalink]
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kntombat wrote:
Sajjad1994 Could you provide the Official Explanation for this question as and when possible ?
Thanks.


Official Explanation

The question is based on the overlapping sets formula. The equation for three group overlapping sets is:

Group 1 + Group 2 + Group 3 - Overlap Exactly Two Groups - 2(Overlap all Three) + None

Following this convention the equation would be 150 = 40 + 50 + 90 - 70 - 2(x) + None

150 = 40 + 50 + 90 - 70 - 0 + 40

Therefore 40 & 0 are the only acceptable options.
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Re: At Rocket Brown Elementary School there are 150 students and three [#permalink]
Sajjad1994 wrote:
kntombat wrote:
Sajjad1994 Could you provide the Official Explanation for this question as and when possible ?
Thanks.


Official Explanation

The question is based on the overlapping sets formula. The equation for three group overlapping sets is:

Group 1 + Group 2 + Group 3 - Overlap Exactly Two Groups - 2(Overlap all Three) + None

Following this convention the equation would be 150 = 40 + 50 + 90 - 70 - 2(x) + None

150 = 40 + 50 + 90 - 70 - 0 + 40

Therefore 40 & 0 are the only acceptable options.



Could you explain why can't it be 80 and 20? Thanks.
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Re: At Rocket Brown Elementary School there are 150 students and three [#permalink]
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Baps wrote:

Could you explain why can't it be 80 and 20? Thanks.


Keep in mind this is an overlapping sets question, we can use the formula given below

Group 1 + Group 2 + Group 3 - Overlap Exactly Two Groups - 2(Overlap all Three) + None

We have total 150 students, if you put 80 and 20 it will exceed 150 and cannot fit into the equation. So we can only pick 40 and 0 and these are only values fits in the formula above.

Thank you
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Re: At Rocket Brown Elementary School there are 150 students and three [#permalink]
150=40+50+90-2*(20)+80

THIS ALSO SATISFIES THE EQUATION. DOESNT IT?
THEN WHY IS NONE=80 AND ALL-3=20 INCORRECT
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Re: At Rocket Brown Elementary School there are 150 students and three [#permalink]
This is very interesting.. below is my rationale for why it cannot be 20 and 80 for ‘all 3’ and ‘none’ respectively.

Let us take ‘all 3’ as 20. In Group 1,Hockey, there are 40 students. Of this 20 are also on the other 2 sports coz of our assumption.

Let us say that the remaining 20 also play Group 2 sports. That would mean, of the 70 who were in exactly 2 games, 20 are in Group 1 and Group 2. This would leave the remaining 50 to be only in Group 2 and Group 3, but this is not possible since Group 2 had a total of 50 students to begin with and of those 20 are in Group 1 & Group 2..

Similarly if you think about all the different overlaps, there is no way to satisfy the 70 ‘2-group’ overlap at all if we assumed ‘all-three’ to be 20… hence why that has to be 0 and naturally the ‘none’ becomes 40.

Equation wise, we also should have 1&2 + 2&3 + 1&3 = 70 or something like that and that will act as a restraining equation giving us this answer or something.

Posted from my mobile device
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Re: At Rocket Brown Elementary School there are 150 students and three [#permalink]
Why can it be the other way round i.e. none = 40 and all three = 0?
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Re: At Rocket Brown Elementary School there are 150 students and three [#permalink]
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