+1 vote
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A gathering of $50$ linguists discovered that $4$ knew Kannada$,$ Telugu and Tamil$,$ $7$ knew only Telugu and Tamil $,$ $5$ knew only Kannada and Tamil $,$ $6$ knew only Telugu and Kannada$.$ If the number of linguists who knew Tamil is $24$ and those who knew Kannada is also $24,$ how many linguists knew only Telugu$?$

1. $9$
2. $10$
3. $11$
4. $8$

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This question has an underlying assumption (albeit logical) that all of the people present speak at least one language.

Let  $K_a$ denote Kannada, $T_a$ denote Tamil and $T_e$ denote Telegu.

$n(K_a \cup T_a \cup T_e ) = n(K_a) + n(T_a) + n(T_e) - n(K_a \cap T_a ) - n(K_a \cap T_e ) - n(T_e \cap T_a ) + n(K_a \cap T_a \cap T_e )$

$\implies 50 = 24 +24 + n(T_e) - (5+4) - (6+4) - (7+4) + 4$

$\implies 50 = 48 + n(T_e) - 26$

$\implies n(T_e) = 28.$

$\therefore$ Number of people who know Telegu, $n(T_e) =28.$

Number of people who know only Telegu

$= n(T_e) - n(K_a \cap T_e ) - n(T_e \cap T_a ) + n(K_a \cap T_a \cap T_e )$

$= 28 -(6+4) -(7+4) +4$

$= 11$

Correct Option: C.
by

Here the ONLY word used in question is important.

$\therefore$ Option $C.$ is correct.

by
edited by
+1

Yes i am also getting the same thing...

https://gateoverflow.in/?qa=blob&qa_blobid=12637213641174896015

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I got 7 too using Venn diagram :O
+1
You should be careful in reading the sentences in question.
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got the right answer now :P