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Re: The average (arithmetic mean) of a, b, c, d, e is 7. What is [#permalink]
28 Jul 2012, 23:43

Expert's post

The average (arithmetic mean) of a, b, c, d, e is 7. What is the average of a, b, c, d, e, f ?

It's almost always better to express the average in terms of the sum. Given: a+b+c+d+e=5*7. Question: a+b+c+d+e+f=? --> 5*7+f=? So basically we are asked to find the value of f.

(1) The average of b, c, d, e, f is 9 --> b+c+d+e+f=5*9. Not sufficient.

(2) The average of b, c, d, e is 11 --> b+c+d+e=4*11. Not sufficient.

(1)+(2) Subtract (2) from (1): f=5*9-4*11=1. Sufficient.