=1 1/19*(2 11/15-3/10-1 1/6)=1 1/19*
(2 22/30-9/30-1 5/30)=1 1/19*1 4/15=
20/19*19/15=4/3=1 1/3
3) 2 11/15•1 1/19-1 1/19•3/10-1 1/6•1 1/19 = 1 1/19 · (2 11/15 - 3/10 - 1 1/6) =
= 20/19 · (2 22/30 - 9/30 - 1 5/30) = 20/19 · 1 8/30 =
= 20/19 · 1 4/15 = 20/19 · 19/15 = 4/3 = 1 1/3
