Step 1: Assume the expenditures. Let the expenditure of Lakshmi be \[ E_L = 2x \] and that of Meenakshi be \[ E_M = 3x. \] Step 2: Use the given ratio of Lakshmi’s income to Meenakshi’s expenditure. It is given that \[ \frac{I_L}{E_M} = \frac{6}{7}. \] Substituting \(E_M = 3x\), \[ \frac{I_L}{3x} = \frac{6}{7} \Rightarrow I_L = \frac{18x}{7}. \] Step 3: Express the savings. Savings are equal to income minus expenditure. Lakshmi’s savings are \[ S_L = I_L - E_L = \frac{18x}{7} - 2x = \frac{18x - 14x}{7} = \frac{4x}{7}. \] Let Meenakshi’s income be \(I_M\). Then her savings are \[ S_M = I_M - 3x. \] Step 4: Apply the ratio of savings. Given that \[ S_L : S_M = 4 : 9, \] we have \[ \frac{\frac{4x}{7}}{I_M - 3x} = \frac{4}{9}. \] Cancelling 4 from both sides, \[ \frac{\frac{x}{7}}{I_M - 3x} = \frac{1}{9}. \] Thus, \[ 9 \cdot \frac{x}{7} = I_M - 3x \Rightarrow I_M = \frac{9x}{7} + 3x = \frac{9x + 21x}{7} = \frac{30x}{7}. \] Step 5: Find the ratio of incomes. \[ \frac{I_L}{I_M} = \frac{\frac{18x}{7}}{\frac{30x}{7}} = \frac{18}{30} = \frac{3}{5}. \] Hence, the ratio of Lakshmi’s income to Meenakshi’s income is \[ 3 : 5. \]
A shopkeeper sells an item at a 20 % discount on the marked price and still makes a 25 % profit. If the marked price is 500 rupees, what is the cost price of the item?
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: