Question 916155
1. 36n the total weight of group originally (concept of average weight)
{{{(36n - 54)/(n-1)}}} = 34   (one weighing 54kg left group) 
36n - 54 = 34n - 34
2n = 20
n = 10 children were there in the group at first. Then 9 when one left.
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2. T being the total of all scores originally
{{{(T + 14)/n = 90}}} concept of Average score  
T + 14 = 90n
{{{(T -4)/n = 88}}} concept of Average score
T - 4 = 88n
Finding n...
T+14 = 90n
<u>-(T-4 = 88n)</u>
18 = 2n
9 = n