When a student weighing 45 kgs left a class, the average weight of the remaining 59 students increased by 200g. What is the average weight of the remaining 59 students?
55
56
57
58
Explanation:
Let the average weight of the 59 students be A.
So, the total weight of the 59 of them will be 59 $\times$ A.
Given that when the weight of this student who left is added, the total weight of the class = 59A + 45
When this student is also included, the average weight decreases by 0.2 kgs.
So,
=> (59A+45)/60 = A-0.2.
=> 59A + 45 = 60A - 12.
=> 45 + 12 = 60A - 59A.
=> A = 57.