Step 1: Use the first selling condition. The cost price is \[ CP = 1650. \] A profit of \(20\%\) gives \[ \text{Profit}_1 = 0.20 \times 1650 = 330. \] Hence, the first selling price is \[ SP_1 = 1650 + 330 = 1980. \] Let the marked price be \(MP\) and the discount be \(D\). Then, \[ MP - D = 1980. \tag{1} \] Step 2: Use the second selling condition. Here, the profit is Rs. \(110\), so the selling price becomes \[ SP_2 = 1650 + 110 = 1760. \] The discount is doubled, so the new discount is \(2D\). Thus, \[ MP - 2D = 1760. \tag{2} \] Step 3: Find the marked price. Subtracting equation (2) from equation (1), \[ (MP - D) - (MP - 2D) = 1980 - 1760, \] which gives \[ D = 220. \] Substituting into equation (1), \[ MP - 220 = 1980 \Rightarrow MP = 2200. \] Step 4: Equate discount percentage and profit percentage. Let the common value of discount percent and profit percent be \(x\). The discount amount is \[ \frac{x}{100} \times 2200 = 22x. \] Hence, the selling price is \[ SP = 2200 - 22x. \] The corresponding profit is \[ \text{Profit} = (2200 - 22x) - 1650 = 550 - 22x. \] Therefore, the profit percentage on cost price is \[ \frac{550 - 22x}{1650} \times 100. \] Since this equals \(x\), \[ x = \frac{550 - 22x}{1650} \times 100. \] Step 5: Solve for \(x\). \[ x = \frac{100(550 - 22x)}{1650} = \frac{550 - 22x}{16.5}. \] Thus, \[ 16.5x = 550 - 22x, \] \[ 38.5x = 550, \] \[ x = \frac{550}{38.5} = \frac{100}{7} \approx 14.29. \] Hence, the required discount rate is approximately \(14\%\).
For any natural number $k$, let $a_k = 3^k$. The smallest natural number $m$ for which \[ (a_1)^1 \times (a_2)^2 \times \dots \times (a_{20})^{20} \;<\; a_{21} \times a_{22} \times \dots \times a_{20+m} \] is: