Question 61
Let $A = \{1, 2, 3, \dots, 2025\}$. A subset $B$ of the set $A$ will be called *nice* if it has 3 elements, one of them being the arithmetic mean of the other two, and there exists $b \in B$ such that $5 \cdot b \in B$.
a) Find how many nice sets have the element $225$.
b) Find how many nice subsets has $A$.
a) Find how many nice sets have the element $225$.
b) Find how many nice subsets has $A$.