( 3+ 1_13/15 ) * ( 1- 1/3) =
=( 3+ 28/15 ) * ( 1- 1/3) =
=3 + 28/15 -1 - 28/(15*3) =
=2 + (28*3-28)/(15*3) =
=2 + 56/45 = 2 + 1_11/45 = 3_11/45 (3 целых 11/45)
ИЛИ
( 3+ 1_13/15 ) * ( 1- 1/3) =
=( 3+ 28/15 ) * 2/3 =
= 2 + 56/45 = 2 + 1_11/45 = 3_11/45 (3 целых 11/45)