Question
The average weight of 40 students in a class is 60 kg. A group of students with average weight 50 kg joins the class, and the overall average becomes 58 kg. How many students are there in the group?
Solution
ATQ, Let x be the number of new students. Initial total weight = 40 × 60 = 2400. New group’s total weight = 50x. New average = 58 ⇒ (2400 + 50x) / (40 + x) = 58 2400 + 50x = 58(40 + x) = 2320 + 58x 2400 − 2320 = 58x − 50x 80 = 8x ⇒ x = 10.
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