Question 771402
    The arithmetic mean of a set of 50 numbers is 38. 
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Therefore it's the same as if every number were 38.
So the sum of the numbers is 50×38 = 1900
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If two numbers 45 and 55 are discarded,  
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That's subtracting them both from the 1900. 1900 - 45 - 55 = 1800.
1800 is the new sum of the numbers after those 100 were discarded.

So now there are only 48 numbers after those two are discarded.
The new average is

{{{1800/48}}} = {{{75/2}}} = 37.5
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the mean of the remaining set of numbers is 37.5.
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Edwin</pre>