Multiple choice

Four years ago, the average age of four friends was 21 years. At present, with a new friend joining the group, their average age is 24 years. What is the present age of the new friend?

  1. 36 years

  2. 20 years

  3. 24 years

  4. 21 years

  5. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Four years ago, the sum of ages of 4 friends was 21 * 4 = 84. At present, their sum is 84 + (4 * 4) = 100. With the new friend, the sum of 5 friends is 24 * 5 = 120. The new friend's age is 120 - 100 = 20.

AI explanation

Using the average formula, the sum of the present ages of the four friends is 21 plus 4 times 4, which equals 100 years. With the new friend included, the sum of the ages of all five friends is 24 times 5, which equals 120 years. The present age of the new friend is the difference between these sums, 120 minus 100, which is 20 years.

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