Multiple choice

In a class of 80 students average age is 19 years and 3 months when 20 students left the class new average age of class becomes 19 years. Find the average age of students who left the class. एक 80 बच्चों की कक्षा की औसत आयु 19 वर्ष तथा 3 माह थी। जब 20 बच्चे कक्षा छोड़कर चले गये तो कक्षा की नयी औसत आयु 19 वर्ष हो गयी। कक्षा छोड़कर जाने वाले बच्चों की औसत आयु ज्ञात कीजिए।

  1. 21 years and 6 months 21 वर्ष और 6 माह

  2. 22 years 22 वर्ष

  3. 21 years 21 वर्ष

  4. 20 years 20 वर्ष

  5. 20 years and 9 months 20 वर्ष और 9 माह
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Total age of 80 students = 80 × 19.25 = 1540 years. After 20 leave, 60 students have total age 60 × 19 = 1140 years. The 20 who left had total age 1540-1140=400 years, so average = 400÷20=20 years. Option C (21 years) is a common error from incorrect subtraction.

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