Multiple choice

Find the average age of 30 students studying in class 5th- Statement I: Ratio of boys and girls in class is 3:2 and difference of total sum age of boys and total sum age of girls is 36 years. Statement II: Average age of girls in class is 11 years and 6 months. Statement III: If 10 new students join the class with an average age of 14 years the new average age of class will increase by 1 year.

  1. Only I

  2. Only III

  3. I and III

  4. All three together

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

Statement III: Let original average = x. Total age = 30x. New total = 30x + 10×14 = 30x + 140. New average = (30x+140)/40 = x+1. Solving: 30x+140 = 40x+40, x = 10. So average = 10. Statements I and II don't uniquely give the answer. Only III is sufficient.

Keep practicing — related questions