A father is 4 times as old as his son. In 20 years, he will be twice as old as his son. How old are they now?, Father: 40 years old, Son: 10 years old. Let son = x → father = 4x. In 20 years: 4x + 20 = 2(x + 20) → x = 10, Four students—A, B, C, and D—rank 1st to 4th. A is not 1st or 4th. B ranks higher than D. C is not 2nd. Who ranks 1st?, Answer is B. Try placements logically: A can only be 2nd or 3rd. C cannot be 2nd. B must be above D. Only consistent ranking: B–A–D–C, I am a two-digit number. The sum of my digits is 10. The difference of my digits is 4. What is the number?, The number is 73. 7 + 3 = 10. 7 − 3 = 4, Find the missing number: 8 → 64, 5 → 25, 9 → ?, The missing number is 81. Each number is squared., Find the next number: 1, 4, 9, 16, ?, The next number is 25. Perfect squares: 1², 2², 3², 4², 5².

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