A two-digit number is 4 times the sum of its digits. If 27 is added to the number, the digits reverse. What is the original number?
Answer and explanation
Correct answer: D. 36
- Step 1: Let number be 10t + u. 10t + u = 4(t + u) => 6t = 3u => u = 2t. Step 2. Reversal: 10t + u + 27 = 10u + t => 9u - 9t = 27 => u - t = 3. Step 3. 2t - t = 3 => t = 3 and u = 6. The number is 36. Answer: 36. Why not the others: 36: sum = 9; 4 * 9 = 36; 36 + 27 = 63.
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