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# 3/4 of all married couples have more than one child. 2/5 of all marrie

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Manager
Joined: 09 Dec 2009
Posts: 119
3/4 of all married couples have more than one child. 2/5 of all marrie  [#permalink]

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17 Feb 2010, 16:25
8
00:00

Difficulty:

35% (medium)

Question Stats:

73% (01:50) correct 27% (02:02) wrong based on 345 sessions

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3/4 of all married couples have more than one child. 2/5 of all married couples have more than 3 children. What fraction of all married couples have 2 or 3 children?

A. 1/5
B.1/4
C. 7/20
D. 3/5
E. It cannot be determined from the given information.

Source: MGMAT.

I'm debating this answer. I understand how they derive it when you make the assumption that ALL married couples have kids but the fact that it DOES NOT explicitly say what fraction of couples have no kids we do not have sufficient to information to conclusively answer the question asked. Am I missing something?

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Senior Manager
Joined: 25 Jun 2009
Posts: 278
Re: 3/4 of all married couples have more than one child. 2/5 of all marrie  [#permalink]

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17 Feb 2010, 16:33
2
Currency wrote:
3/4 of all married couples have more than one child. 2/5 of all married couples have more than 3 children. What fraction of all married couples have 2 or 3 children?

A. 1/5
B.1/4
C. 7/20
D. 3/5
E. It cannot be determined from the given information.

Source: MGMAT.

I'm debating this answer. I understand how they derive it when you make the assumption that ALL married couples have kids but the fact that it DOES NOT explicitly say what fraction of couples have no kids we do not have sufficient to information to conclusively answer the question asked. Am I missing something?

I guess its right, lets take step by step, Lets assume there are 100 couple in total

now according to the question stem 3/4 of all married couples have more than one child
i.e 75 couples have more than one child and rest of them (25 couples have either one or none )

second part of the question says 2/5 of all married couples have more than 3 children
i.e 40 couples have 3 + children.

Question asks us to calculate couple with either or 2 or 3 children.

now we know 25 couples have either one or none children and 35 ( 75-40) have either 2 or 3 children

Hence 35/100 = 7/20 is the answer.

To add on to it we explicitly dont have to calculate how many couples have 0 kids we just need the number of couples who have 2 or 3 kids which can be calculated as shown above.

I hope that helps.
Senior Manager
Joined: 21 Jul 2009
Posts: 327
Schools: LBS, INSEAD, IMD, ISB - Anything with just 1 yr program.
Re: 3/4 of all married couples have more than one child. 2/5 of all marrie  [#permalink]

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17 Feb 2010, 16:35
1
2
Currency wrote:
3/4 of all married couples have more than one child. 2/5 of all married couples have more than 3 children. What fraction of all married couples have 2 or 3 children?

A. 1/5
B.1/4
C. 7/20
D. 3/5
E. It cannot be determined from the given information.

Source: MGMAT.

I'm debating this answer. I understand how they derive it when you make the assumption that ALL married couples have kids but the fact that it DOES NOT explicitly say what fraction of couples have no kids we do not have sufficient to information to conclusively answer the question asked. Am I missing something?

Plug in simple numbers. Take 100 couples for example.

3/4 of 100 couples have more than one child = 75 couples.
2/5 of 100 couples have more than 3 kids = 40 couples.
This implies that 40 couples are a subset of 75 couples and the complement of 75 couples within those 100 couples, which equals 25 couples have either one or no kids at all.
We need to find couples that have 2 or 3 kids, so essentially, it is 75 - 40 = 35. Fraction will be 35/100 = 7/20.
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Manager
Joined: 10 Feb 2010
Posts: 155
Re: 3/4 of all married couples have more than one child. 2/5 of all marrie  [#permalink]

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17 Feb 2010, 17:48
C

100 Married couples.

1 or more = 75
4 or more = 40
2 or 3 = 75-40 = 35

35/100 = 7/20
Manager
Joined: 09 Dec 2009
Posts: 119
Re: 3/4 of all married couples have more than one child. 2/5 of all marrie  [#permalink]

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17 Feb 2010, 18:42
Thanks fellas. I see the solution now. Makes sense when you grind it out.

One of my trouble spots is not fully grinding out a problem when I believe it to be unsolvable after reading thru the question. I get this more on DS questions.

In any event, thanks for the help!
_________________

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Round 2: 07/10/10 - This time it's personal.

Manager
Joined: 01 Feb 2010
Posts: 233
Re: 3/4 of all married couples have more than one child. 2/5 of all marrie  [#permalink]

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18 Feb 2010, 07:39
1
Couples with two or three children = 3/4 - 2/5 = 7/20 hence C.
Manager
Joined: 10 Feb 2010
Posts: 155
Re: 3/4 of all married couples have more than one child. 2/5 of all marrie  [#permalink]

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18 Feb 2010, 19:19
Currency wrote:
Thanks fellas. I see the solution now. Makes sense when you grind it out.

One of my trouble spots is not fully grinding out a problem when I believe it to be unsolvable after reading thru the question. I get this more on DS questions.

In any event, thanks for the help!

By practicing, you will be able to think thru logically while reading the question. Also, just reading the questions on the forums and solving helps a lot!
Senior SC Moderator
Joined: 14 Nov 2016
Posts: 1321
Location: Malaysia
3/4 of all married couples have more than one child. 2/5 of all marrie  [#permalink]

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27 Jan 2017, 07:35
TheSituation wrote:
3/4 of all married couples have more than one child. 2/5 of all married couples have more than 3 children. What fraction of all married couples have 2 or 3 children?

A. 1/5
B.1/4
C. 7/20
D. 3/5
E. It cannot be determined from the given information.

Source: MGMAT.

I'm debating this answer. I understand how they derive it when you make the assumption that ALL married couples have kids but the fact that it DOES NOT explicitly say what fraction of couples have no kids we do not have sufficient to information to conclusively answer the question asked. Am I missing something?

This fraction problem contains an unspecified total (the number of married couples) and is most easily solved by a picking a "smart" number for that total. The smart number is the least common denominator of all the fractions in the problem. In this case, the smart number is 20.

Let's say there are 20 married couples.
15 couples ( $$\frac{3}{{4}}$$ of the total) have more than one child.
8 couples ( $$\frac{2}{{5}}$$ of the total) have more than three children.
This means that 15 – 8 = 7 couples have either 2 or 3 children. Thus 7/20 of the married couples have either 2 or 3 children.

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Senior Manager
Joined: 15 Jan 2017
Posts: 355
Re: 3/4 of all married couples have more than one child. 2/5 of all marrie  [#permalink]

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12 Dec 2017, 13:28
3/4 of all married couples have more than one child. 2/5 of all married couples have more than 3 children. What fraction of all married couples have 2 or 3 children?

Followed this method:

3/4 (MC) = x +1 (more than 1 kid)

2/5 (MC) = x + 2 (more than 3 kids)

between 2 or 3 kids.

3/4 (larger number) - 2/5 (smaller number) --> More than 1 (3/4) - More than 3 (2/5)= 7/20 (between 2 - 3)

[Think of it like a concentric rings with the same outer circle --> largest inner circle will be 3/4 and smallest 2/5. The in between portion is what we need]

Kudos, if this post made sense
Intern
Joined: 24 Jul 2018
Posts: 8
Re: 3/4 of all married couples have more than one child. 2/5 of all marrie  [#permalink]

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02 Aug 2018, 17:06
TheSituation wrote:
3/4 of all married couples have more than one child. 2/5 of all married couples have more than 3 children. What fraction of all married couples have 2 or 3 children?

A. 1/5
B.1/4
C. 7/20
D. 3/5
E. It cannot be determined from the given information.

Source: MGMAT.

I'm debating this answer. I understand how they derive it when you make the assumption that ALL married couples have kids but the fact that it DOES NOT explicitly say what fraction of couples have no kids we do not have sufficient to information to conclusively answer the question asked. Am I missing something?

+1 for C

Among the married:
3/4: > 1 child (2,3,4,5, and above)
2/5: > 3 child (4,5, and above)

=> 3/4 - 2/5 have 2 or 3 children
3/4 - 2/5 = 15/20 - 8/20 = 7/20
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Re: 3/4 of all married couples have more than one child. 2/5 of all marrie &nbs [#permalink] 02 Aug 2018, 17:06
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