Of the 3 numbers whose average is 40, the first is 1/3 rd the sum of other 2. What is the first number?
Let those numbers are A, B, C
(A+B+C)/3 = 40 ---> A+B+C = 120-------(1)
A = (1/3)(B+C) ----> 3A = B+C -------(2)
substitute (2) in (1)
A+3A = 120
4A = 120
A = 30
So the answer is option D.
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