Question:
Let $\bigcup_{i=1}^{50} X_{i}=\bigcup_{i=1}^{n} Y_{i}=T$, where each $X_{i}$ contains 10 elements
and each $Y_{i}$ contains 5 elements. If each element of the set $T$ is an element of exactly 20 of sets $X_{i}^{\prime}$ s and exactly 6 of sets $Y_{i}^{\prime}$ s, then $n$ is equal to
Correct Option: , 4
Solution:
$\bigcup_{i=1}^{50} X_{i}=\bigcup_{i=1}^{n} Y_{i}=T$
$\because \quad n\left(X_{i}\right)=10, n\left(Y_{i}\right)=5$
So, $\bigcup_{i=1}^{50} X_{i}=500, \bigcup_{i=1}^{n} Y_{i}=5 n$
$\Rightarrow \frac{500}{20}=\frac{5 n}{6} \Rightarrow n=30$
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