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2014-08-12T13:41:56+03:00
0,(1x)= (10+x)/99
0,(2x)=(20+x)/99
0,(3x)=(30+x)/99
...........................
0,(9x)=(90+x)/99

(10+x)/99+ (20+x)/99 + (30+x)/99 +....+(90+x)/99=x  aducem la acelasi numitor

10+x+20+x+30+x+...+90+x=99x

9x+(10+20+30+...+90)=99x

9x+ (10+90)*9/2= 99x

9x +100*9/2=99x

9x +50*9=99x

9x +450 =99x

9x -99x= -450

-90x = -450

90x=450

x=5