Multiple choice

Average age of A,B,C,D is $15$ years.A's age is twice that of B,B's age is twice that of C &C's age is twice that of D. What is present age of B?

  1. $4$ yrs.
  2. $8$ yrs.
  3. $16$ yrs.
  4. $32$ yrs.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let D = x. Then C = 2x, B = 4x, and A = 8x. The average age is (8x + 4x + 2x + x) / 4 = 15, which simplifies to 15x / 4 = 15, so x = 4. Since B = 4x, B is 16 years old.

AI explanation

Let the present age of D be x years, making the ages of C, B and A equal to 2x, 4x and 8x respectively. The sum of their ages is x plus 2x plus 4x plus 8x, which equals 15x. Since the average age is 15 years, their total age is 4 times 15, or 60 years. Setting 15x equal to 60 gives x equals 4, so the present age of B is 4x, which is 16 years.

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