Multiple choice

John is $1$ year younger than his brother David. If the product of their ages is $56$. Find the age of David.

  1. $5$
  2. $6$
  3. $7$
  4. $8$
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D Correct answer
Explanation

Let David's age be x. Then John's age is x - 1. The product is x(x - 1) = 56, which simplifies to x^2 - x - 56 = 0. Factoring gives (x - 8)(x + 7) = 0, so x = 8.

AI explanation

Let David's age be x years, so John's age is x - 1 years. The product of their ages gives the equation x(x - 1) = 56, which simplifies to x squared minus x minus 56 equals 0. Factoring this quadratic equation yields (x - 8)(x + 7) = 0, giving the positive solution x = 8. Therefore, David is 8 years old.

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