x= 1/2 - 1/3 +1/4 -1/5+....... + 1/2002 - 1/2003;
y= 1 -1/2 + 1/3 - 1/4+........ +1/2001 - 1/2002
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x + y = 1 + 0 + 0 + 0 + ........................ + 0 -1 / 2003
x + y = 1 - 1 / 2003 = ( 2003 - 1 ) / 2003 = 2002 / 2003
med. arit. = ( x + y) / 2 = 2002 / 2003 · 2 = 1001 / 2003