Question 316008
The mean of five numbers is 6.  If one of the numbers is removed, the mean becomes 7.  What is the value of the number that was removed? 
<pre><b>
{{{Mean = Sum/n}}}

{{{ 6 = Sum/5}}}

{{{30 = Sum}}}

Let R = the number that was removed.

Then the new Sum after removing R was 30-R

Going back to

{{{Mean = Sum/n}}}

{{{ 7 = (30-R)/4}}}

{{{28 = 30-R}}}

{{{R = 30-28}}}

{{{R=2}}}

So 2 was removed.

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Suppose the 5 numbers were 2, 5, 6, 8, 9

Their mean is {{{(2+5+6+8+9)/5=30/5=6}}}

If we remove the 2, the numbers left are 5, 6, 8, 9

Their mean is {{{(5+6+8+9)/4 = 28/4 = 7}}}

So we know we are right that 2 was removed.

Edwin</pre>