SOLUTION: The mean of a set of numbers is 120. If one number is increased by 300, the mean equals 135. How many numbers are in the set?

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Question 359419: The mean of a set of numbers is 120. If one number is increased by 300, the mean equals 135. How many numbers are in the set?
Answer by jrfrunner(365) About Me  (Show Source):
You can put this solution on YOUR website!
average = sum%28x%29%2Fn therefore
n%2Aaverage=sum%28x%29
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given
average=120 then we have the relationship n%2A120=sum%28x%29
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also if one number is increased by 300 (this means that sum%28x%29 increases by 300) and the average =135
thus n%2A135=sum%28x%29%2B300
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So you have two equations and two unknowns, solve for n
n%2A120=sum%28x%29
n%2A135=sum%28x%29%2B300
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n%2A135-n%2A120=sum%28x%29%2B300-sum%28x%29 subtract the second equation from the first
15n=300
n=300/15=20