(1\5-1\6)-(1\10-1\6)-(1\20-1\10)
(1/5-1/6)-(1/10-1/6)-(1/20-1/10)= (6/30-5/30)-(3/30-5/30)-(2/40-4/40)= 1/30+2/30+2/40=3/30+2/40= =12/120+6/120=6/120=1/20=0,05