Task:
If |A| = 30 and equivalence R on A induces three partitions $A_1$, $A_2$, $A_3$ and |$A_1$| = |$A_2$| = |$A_3$|, what is |R|?
My solution is $|R| = 300$. I know that count of elements in partitions is $10$ and then every pair need to be connected with other $9$ pairs and plus 10 because of maintaining reflexivity, so it is $3 * (10 * 9 + 10)$. Is this correct?