In a school, the average age of students is 6 years, and the average age of 12 teachers is 40 years. If the average age of the combined group of all the teachers and students is 7 years, then the number of students is :
Options:
A . 400
B . 396
C . 416
D . 408
Answer: Option B Answer: (b)Let the number of students be n. Then, 7 = ${n × 6 + 12 × 40}/{n + 12}$⇒ 7n + 84 = 6n + 480⇒ n = 480 – 84 = 396
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