waecmaths question:
Every staff in an office owns either a Mercedes or Toyota car. 20 owns Mercedes, 15 own Toyota and 5 own both. How many staff are there in the office?
Option A:
15
Option B:
30
Option C:
35
Option D:
45
waecmaths solution:
$\begin{align} & n(M)=20 \\ & n(T)=15 \\ & n(M\cap T)=5 \\ & n(M\cup T)=n(M)+n(T)-n(M\cap T) \\ & n(M\cup T)=20+15-5=30 \\\end{align}$
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