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Cat face : (x+2x3x+...+403x):202 =2015 ?

Răspuns :

[tex](x+2x+3x+...+403x):202 =2015 \\ x(1+2+3+...+403):202=2015 \\ x * \frac{403 *404}{2} * \frac{1}{202} =2015 \\ x* \frac{403*202}{202} =2015 \\ x= 2015:403=5 [/tex]