Step 1: Convert credit price to cash equivalent.
Present value of ₹ 2200 due in $1$ year at $10\%$ p.a.:
$\text{PV}=\dfrac{2200}{1+0.10}=₹ 2000$.
Step 2: Compare with cost.
Effective SP (cash equivalent) $=₹ 2000$, Cost $=₹ 1950$.
Gain $=₹(2000-1950)=₹ 50$.
\Rightarrow\ \boxed{\text{Gains ₹ 50}}.