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Number of elements in R1 - R2 for two relations on a set

This type of question, asked 2 times: 28 Jun 2022, 1 Feb 2024. All 2 questions below, oldest first.

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  1. Question 1

    28 Jun 2022

    81
    Let R1R_{1} and R2R_{2} be relations on the set {1,2,…,50}\mathbf{\{ 1,2,\ldots,50\}} such that R1={(p,pn):pR_{1}=\left\{ \left( p,p^{n} \right):p \right. is a prime and n≥0n \geq 0 is an integer }\} and R2={(p,pn):pR_{2}=\left\{ \left( p,p^{n} \right):p \right. is a prime and n=0n= 0 or 1}\}. Then, the number of elements in R1−R2R_{1}-R_{2} is

  2. Question 2

    1 Feb 2024

    90
    Let A={1,2,3,…20}\mathbf{A = \{ 1,2,3,\ldots 20\}}. Let R1R_{1} and R2R_{2} two relation on A such that R1={(a,b):bR_{1}\mathbf{= \{(a,b):b} is divisible by a}a\} R2={(a,b)R_{2}\mathbf{= \{(a,b)} : aa is an integral multiple of b}b\}. Then, number of elements in R1−R2R_{1}-R_{2} is equal to