Let A = {1,2,3, ... , 20}. Let $R\subseteq A\times A$ such that R = {(x,y): y = 2x - 7}. Then the number of elements in R, is equal to

Given relation: $R = \{(x,y) : y = 2x - 7\}$ where $A = \{1,2,3,\dots,20\}$.

We need both $x, y \in A$.

So, $1 \le y = 2x - 7 \le 20$

⇒ $1 \le 2x - 7 \le 20$

Add 7: $8 \le 2x \le 27$

Divide by 2: $4 \le x \le 13.5$

Hence, integer values of $x$ are $4,5,6,7,8,9,10,11,12,13$ → total $10$ values.

✅ Number of elements in R = 10