Question
In a class of 40 students, the average weight is 72 kg.
One student of weight 68 kg left and three new students with an average weight of 75 kg joined the class. When a teacher’s weight is also included, the average weight of the class becomes 74 kg. What is the weight of the teacher?Solution
Initial total weight of the class = 40 × 72 = 2880 kg
The sum of weight of 3 new students = 3 × 75 = 225 kg Let the weight of the teacher be ‘y’ kg.
New total weight of the class without teacher = 2880 - 68 + 225 + y = (3037 + y) kg
New total number of people = 40 - 1 + 3 + 1 = 43
New total weight of the class with teacher = 74 × 43 = 3182 kg
So, weight of the teacher = 3182 - 3037 = 145 kg
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