If sales is Rs. 2,40,000, Gross Profit is 1/3 of cost, purchases is Rs. 1,96,000 and closing stock is…

A gross profit of $\frac{1}{3}$ of cost equals $\frac{1}{4}$ of sales, which is $\frac{2{,}40{,}000}{4} = \text{Rs. } 60{,}000$, so Cost of Goods Sold (COGS) is $2{,}40{,}000 - 60{,}000 = \text{Rs. } 1{,}80{,}000$. Since $\text{COGS} = \text{Opening Stock} + \text{Purchases} - \text{Closing Stock}$, we have $1{,}80{,}000 = \text{Opening Stock} + 1{,}96{,}000 - 36{,}000$, giving Opening Stock of "Rs. 20,000".