Step 1: Apply the present value concept. The amount of the loan is equal to the present value of the future installments. Hence, \[ 1000 = \frac{530}{1+r} + \frac{594}{(1+r)^2}. \] Let \[ x = 1 + r. \] Then the equation becomes \[ 1000 = \frac{530}{x} + \frac{594}{x^2}. \] Step 2: Eliminate denominators. Multiplying both sides by \(x^2\), \[ 1000x^2 = 530x + 594. \] Rewriting, \[ 1000x^2 - 530x - 594 = 0. \] Dividing throughout by \(2\) for simplification, \[ 500x^2 - 265x - 297 = 0. \] Step 3: Solve the quadratic equation. For the equation \(500x^2 - 265x - 297 = 0\), \[ a = 500,\quad b = -265,\quad c = -297. \] Using the quadratic formula, \[ x = \frac{265 \pm \sqrt{(-265)^2 - 4(500)(-297)}}{1000}. \] Evaluating the discriminant, \[ (-265)^2 = 70225,\qquad 4 \cdot 500 \cdot 297 = 594000, \] \[ 70225 + 594000 = 664225 = 815^2. \] Thus, \[ x = \frac{265 \pm 815}{1000}. \] Taking the positive root, \[ x = \frac{1080}{1000} = 1.08. \] (The negative root is rejected since \(x = 1+r > 0\).) Step 4: Determine the rate of interest. \[ 1 + r = 1.08 \Rightarrow r = 0.08. \] Therefore, the rate of interest is \(8\%\).
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: