JEE Mains · Maths · STD 12 - 1. relation and function
Let \(A=\{1,2,3, \ldots 20\}\). Let \(R_1\) and \(R_2\) two relation on \(\mathrm{A}\) such that \(\mathrm{R}_1=\{(\mathrm{a}, \mathrm{b}): \mathrm{b}\) is divisible by \(\mathrm{a}\}\) \(\mathrm{R}_2=\{(\mathrm{a}, \mathrm{b}): \mathrm{a}\) is an integral multiple of \(\mathrm{b}\}\). Then, number of elements in \(R_1-R_2\) is equal to ...........
- A \(44\)
- B \(46\)
- C \(45\)
- D \(40\)
Answer & Solution
Correct Answer
(B) \(46\)
Step-by-step Solution
Detailed explanation
\( \mathrm{n}\left(\mathrm{R}_1\right)=20+10+6+5+4+3+2+2+2 \) \( +2+\underbrace{1+\ldots+1}_{10 \text { times }}\) \(\mathrm{n}\left(\mathrm{R}_1\right)=66\) \(\mathrm{R}_1 \cap \mathrm{R}_2=\{(1,1),(2,2), \ldots(20,20)\}\)…
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