SOLUTION: the average of first three numbers is double from fourth no. if the average of all four number is 28 find out the fourth number

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Question 1023101: the average of first three numbers is double from fourth no. if the average of all four number is 28 find out the fourth number
Answer by god2012(113) About Me  (Show Source):
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Let the numbers be a,b,c and d.
Average of first 3 numbers is double the 4th
(a+b+c)/3 = 2d => (a+b+c) = 6d -----------eq.1
Avg. of all 4 numbers is
(a+b+c+d)/4 = 28 => /(a+b+c+d) = 28*4 = 112 ----eq.2
Put eq.1 in eq.2
6d + d = 112
7d = 112
d = 112/7
d = 16
So, the 4th number is 16