Question:
A relation \( r(A,B) \) has 1200 tuples.
Attribute \( A \) ranges from 6 to 20 and attribute \( B \) ranges from 1 to 20. Assume independent uniform distribution. The estimated number of tuples in \( \sigma_{(A>10)\vee(B=18)}(r) \) is \(\underline{\hspace{2cm}}\).
A relation \( r(A,B) \) has 1200 tuples.
Attribute \( A \) ranges from 6 to 20 and attribute \( B \) ranges from 1 to 20. Assume independent uniform distribution. The estimated number of tuples in \( \sigma_{(A>10)\vee(B=18)}(r) \) is \(\underline{\hspace{2cm}}\).
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For OR conditions, always subtract the intersection probability.
Updated On: Jan 30, 2026
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Verified By Collegedunia
Correct Answer: 819 - 820
Solution and Explanation
\[
P(A>10) = \frac{10}{15}, P(B=18) = \frac{1}{20}
\]
\[
P((A>10)\vee(B=18)) = P(A>10) + P(B=18) - P(A>10)P(B=18)
\]
\[
= \frac{10}{15} + \frac{1}{20} - \frac{10}{15}\times\frac{1}{20}
\]
\[
= 0.6667 + 0.05 - 0.0333 = 0.6834
\]
\[
\text{Estimated tuples} = 1200 \times 0.6834 \approx 820
\]
Final Answer:
\[
\boxed{820}
\]
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