Question

Out of $40$ children $30$ can swim, $27$ can play chess and $5$ can't nothing. How many children can swim only?

• A. $30$
• B. $22$
• C. $12$
• D. $8$

Answer 1

The correct option is D $8$

let the total number of children be $S,A$ be the children who can swim ,$B$ be the children who can play chess and $C$ the children who can do nothing

$n\left(S\right)=40$

$n\left(A\right)=30$

$n\left(B\right)=27$

$n\left(C\right)=5$

$A\cup B=n\left(S\right)-n\left(C\right)=40-5=35$

$A\cap B=n\left(A\right)+n\left(B\right)-n(A\cup B)$

$=30+27-35$

$=22$

Student who can swim only

$n\left(Aonlyswim\right)=n\left(A\right)-(A\cap B)$

$=30-22$

$=8$