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

Question

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

A) 12

B) 17

C) 23

D) 29

E) 31

chetan2u · Answer

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

ENGRTOMBA2018 · Answer

2016-01-09_12-24-54.jpg 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.

TeymurHajiyev · Answer

Thank you, guys! You've done an awesome job!

chesstitans · Answer

hi, do you have more similar questions like this? I really like the such kind of question.

Bunuel · Answer

Data Sufficiency Questions on Overlapping Sets  
   Problem Solving Questions on Overlapping Sets

Hope it helps.

shashankism · Answer

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

CAMANISHPARMAR · Answer

Let the number of students who know English be E

Let the number of students who know French be F

Let the total be "T"

We get two equations from the information:-

1) 0.7E + F = T
2) E + 0.6F = T

Therefore 4F = 3E or F = 3E/4

Substituting the value of F in one of the equations we get:-

T = 29E/20

Therefore, if E = 20 then T = 29

None of the other options are valid as T has to be a whole number.

Option D is the correct answer.

bumpbot · Answer

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

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