waecmaths question:
The venn diagram show the number of students in a class who like reading(R), dancing (D) and swimming (S). How many students like dancing and swimming?
Option A:
7
Option B:
9
Option C:
11
Option D:
13
waecmaths solution:
$\begin{align} & n(D\cap S'\cap R')=3 \\ & n(S'\cap D\cap R)=7 \\ & n(S\cap R\cap D)=2 \\ & n(D\cap S\cap R')=x \\ & n(D)=17 \\ & n(D)=17=2+3+7+x \\ & x=n(D\cap S\cap R')=5 \\ & n(D\cap S)=n(S\cap R\cap D)+n(D\cap S\cap R') \\ & n(D\cap S)=2+5=7 \\\end{align}$
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