Step 1: Convert the holding cost to a yearly figure.
Holding cost is given per month, so \(C_h = 0.50 \times 12 = 6\) rupees per unit per year.
Step 2: Write down the other EOQ inputs.
Annual demand \(D = 10000\) units, ordering cost \(C_o = 550\) rupees per order.
Step 3: Apply the EOQ formula.
\(EOQ = \sqrt{\dfrac{2 D C_o}{C_h}} = \sqrt{\dfrac{2 \times 10000 \times 550}{6}} = \sqrt{1833333.3}\).
Step 4: Take the square root and round.
\(EOQ \approx 1354.0\) units, which rounds to the nearest integer as 1354.
Final Answer:
The optimal lot size is close to 1354 units per order.
\[ \boxed{EOQ \approx 1354} \]