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There are 30 coins in a bag of which 10 are gold. If 25 of the coins a

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There are 30 coins in a bag of which 10 are gold. If 25 of the coins a  [#permalink]

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New post Updated on: 29 Jan 2019, 10:25
1
3
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

74% (01:13) correct 26% (01:32) wrong based on 46 sessions

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There are 30 coins in a bag of which 10 are gold. If 25 of the coins are rare, then the number of rare gold coins in the bag could be any number from

A) 3 to 5
B) 3 to 10
C) 5 to 10
D) 10 to 15
E) 10 to 25

Originally posted by sameer986 on 29 Jan 2019, 10:08.
Last edited by Bunuel on 29 Jan 2019, 10:25, edited 1 time in total.
Renamed the topic.
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Re: Please help me out with this 'Sets' question!  [#permalink]

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New post 29 Jan 2019, 10:26
1
sameer986 wrote:
Q) There are 30 coins in a bag of which 10 are gold. If 25 of the coins are rare, then the number of rare gold coins in the bag could be any number from

A) 3 to 5
B) 3 to 10
C) 5 to 10
D) 10 to 15
E) 10 to 25


Whenever you do such questions, try to identify what you want to find

number of rare gold coins

this means that there will be gold coins and there will be gold coins which wont be rare

Now just read the question and see what all was given

here are 30 coins in a bag of which 10 are gold. If 25 of the coins are rare

--------R--------NR-----
G------6---------4-----10
NG----19--------1-----20
-------25--------5-----30

Now as you can see we need to maximize and minimize the value which can give you 10 Gold coins

6,4
7,3
8,2
9,1

That is the range and Only C satisfies that
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Re: There are 30 coins in a bag of which 10 are gold. If 25 of the coins a  [#permalink]

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New post 31 Jan 2019, 15:22
1
sameer986 wrote:
There are 30 coins in a bag of which 10 are gold. If 25 of the coins are rare, then the number of rare gold coins in the bag could be any number from


the range constrain is \(5\leq raregold \leq 10\)
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Re: There are 30 coins in a bag of which 10 are gold. If 25 of the coins a  [#permalink]

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New post 31 Jan 2019, 19:51
Using a two-by-two table is simple. Substitute the numbers in the both category and try them out.
I'm trying to do it using the overlapping sets formula: Gold+Rare-Both+Neither=Total. It's limited as it doesn't restrict the number in both and neither.

There's the A+B+C+D+E+F+G formula when there are 3 overlapping sets

Is there a formula that is more accurate than both that avoids the need for the two-by-two square?
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Re: There are 30 coins in a bag of which 10 are gold. If 25 of the coins a   [#permalink] 31 Jan 2019, 19:51
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