1)... 0,5(1/3+1/9-1/6)=1/2 * [(6+2-3):(18)]=1/2 * 5/18 = 5 / 36 ;
2)... 1 / 2004 - (1 / 2004 - 1 / 2005) - (1 / 2005 - 1 / 2006) =
= 1/2004 -1/2004+1/2005+1/2005+1/2006 = 1 / 2006 ;
3)... (1/2 + 5/6 - 3/4 ):7/300=[ (6+10-9) / 12] * 300 / 7 =
=7 / 12 * 300 / 7 =300 :12 = 25 ;