If the average (arithmetic mean) of \(x, y\) and \(15\) is \(9,\) and the average of \(x, 2y\) and \(2\) is \(7,\) then \(y =\)
A. 5
B. 6
C. 7
D. 8
E. 9
Answer: C
Source: Magoosh
If the average (arithmetic mean) of \(x, y\) and \(15\) is \(9,\) and the average of \(x, 2y\) and \(2\) is \(7,\) then
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Solution:
We can create the equations:
(x + y + 15)/3 = 9
and
(x + 2y + 2)/3 = 7
Subtracting the first equation from the second, we have:
(y - 13)/3 = -2
y - 13 = -6
y = 7
Answer: C
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