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Students in certain group know either English or French or both. If 30

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Students in certain group know either English or French or both. If 30  [#permalink]

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New post 09 Jan 2016, 07:41
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D
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Question Stats:

47% (03:16) correct 53% (02:49) wrong based on 100 sessions

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Students in certain group know either English or French or both. If 30% of those who know English know French, and 60% of those who know French do not know English, which of the following could be the number of students in the group?

A) 12

B) 17

C) 23

D) 29

E) 31
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Posts: 7556
Re: Students in certain group know either English or French or both. If 30  [#permalink]

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New post 09 Jan 2016, 10:27
1
TeymurHajiyev wrote:
Students in certain group know either English or French or both. If 30% of those who know English know French, and 60% of those who know French do not know English, which of the following could be the number of students in the group?

A) 12

B) 17

C) 23

D) 29

E) 31


Hi,
venn diag would make it easy to comprehend..

let students who Know only english =E..
let students who Know only french =F..
let students who Know both english and french = B..

total =E+F+B..
1) If 30% of those who know English know French..
this means that 30% of students knowing english is B..
B=.3(E+B)...
7B=3E..
\(E=7B/3\)...(i)

2)60% of those who know French do not know English
or .6(F+B)= F..
6B=4F..
\(F=\frac{3B}{2}\)..(ii)

add values found in (i) and (ii) in total..
so \(Total=E+F+B=\frac{7B}{3}+ \frac{3B}{2} + B= \frac{29}{6} * B\)...

Total has to be an integer.. so
Total as \(\frac{29B}{6}\)... gives min value of B as 6 and Total as 29..
ans D
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Re: Students in certain group know either English or French or both. If 30  [#permalink]

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New post 09 Jan 2016, 10:29
1
TeymurHajiyev wrote:
Students in certain group know either English or French or both. If 30% of those who know English know French, and 60% of those who know French do not know English, which of the following could be the number of students in the group?

A) 12

B) 17

C) 23

D) 29

E) 31


Attachment:
2016-01-09_12-24-54.jpg
2016-01-09_12-24-54.jpg [ 25.29 KiB | Viewed 1680 times ]


Refer to the above screenshot for description of the variables. Text in black is given information while the text in red denotes values calculated.

From the picture, NF = 0.7E ....(1)

and from the fact that 60% of french learners do learn english as well ---> 0.3E=0.4F --> 3E=4F ...(2)

Finally, T=F+NF = F+0.7E ...(3)

Substituting the value of E from (2), you get T = 29F/15. Now as Total number of students MUST BE INTEGERS, one way to ensure that is to assume F = multiple of 15 = 15 (as example), giving you T = 29 as 1 possible value.

Thus, D is the correct answer.

Hope this helps.
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Re: Students in certain group know either English or French or both. If 30  [#permalink]

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New post 10 Jan 2016, 05:09
Thank you, guys! You've done an awesome job!
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Re: Students in certain group know either English or French or both. If 30  [#permalink]

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New post 17 Apr 2017, 15:37
TeymurHajiyev wrote:
Thank you, guys! You've done an awesome job!


hi, do you have more similar questions like this? I really like the such kind of question.
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Re: Students in certain group know either English or French or both. If 30  [#permalink]

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New post 17 Apr 2017, 21:26
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Re: Students in certain group know either English or French or both. If 30  [#permalink]

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New post 02 Aug 2017, 02:56
1
TeymurHajiyev wrote:
Students in certain group know either English or French or both. If 30% of those who know English know French, and 60% of those who know French do not know English, which of the following could be the number of students in the group?

A) 12

B) 17

C) 23

D) 29

E) 31


Students know either English or French or both

30% of those who know English know French
60% of those who know French do not know English -> 40% of those who know French know English.

Let the no. of people who know English be x. So the people who knows both = 0.3x
and the number of people who know french be y. So the people who knows both = 0.4y

0.3x = 0.4y
x = 4y/3

Total number of people = x + y - 0.4y = 4y/3 + y -4/10 y = 7y/3 - 2/5y = 29y/15.

So total number of people must be a multiple of 29

Answer D
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Re: Students in certain group know either English or French or both. If 30   [#permalink] 02 Aug 2017, 02:56
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