Step 1: Understand the Condition

Since the article is sold at its marked price without any discount, the selling price equals the marked price ($SP = MP$). The profit made is 18%.

$SP = MP = 826$

Step 2: Relate Cost Price and Marked Price

The formula connecting Cost Price ($CP$) and Selling Price ($SP$) with profit percentage is given by $SP = CP \times \left(1 + \frac{\text{Profit}\%}{100}\right)$.

$826 = CP \times \left(1 + \frac{18}{100}\right)$

Step 3: Solve for Cost Price

Simplify the expression and solve for $CP$: $826 = CP \times 1.18$, which gives $CP = \frac{826}{1.18} = 700$.

$CP = \frac{826}{1.18} = 700$