Multiple choice

The average weight of some students in a class was 69.5 kg. When 10 students of average weight 68 kg joined the class, and 6 students of average weight 60 kg left the class, it was noted that the average weight of the new group of students increased by 2 kg. How many students are there in the class now? एक कक्षा में कुछ विद्यार्थियों का औसत भार 69.5 किग्रा था। जब 68 किग्रा के औसत वजन वाले 10 छात्र कक्षा में शामिल हुए और 60 किग्रा के औसत वजन के 6 छात्रों ने कक्षा छोड़ दी, तो यह देखा गया कि छात्रों के नए समूह के औसत वजन में 2 किग्रा की वृद्धि हुई। अब कक्षा में कितने विद्यार्थी हैं?

  1. 12

  2. 21

  3. 23

  4. 17

  5. None of these इनमें से कोई नहीं

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let n be original students. Total weight = 69.5n. After 10 join (avg 68kg) and 6 leave (avg 60kg), new count = n+4 and new avg = 71.5kg. Equation: 69.5n + 10×68 - 6×60 = 71.5(n+4). Solving: 69.5n + 320 = 71.5n + 286, so 2n = 34, n = 17. Current students = 17+4 = 21. Option B is correct. Option A doesn't account for all changes, C and D are calculation errors.