3 2/5 · 1 4/7 + 2 3/7 · 3 2/5 - 13 3/5 · 1/2 =
= 3 2/5 · (1 4/7 + 2 3/7) - 13 3/5 · 1/2 =
= 3 2/5 ·(3 7/7) - 13 3/5 · 1/2 =
3 2/5 ·4 - 13 3/5 · 1/2 =
= 17/5 · 4 - 68/5 · 1/2 =
= 17/5 ·4 - (4 · 17/5) · 1/2 =
= 17/5 (4 - 4 ·1/2) =
= 17/5 · (4 - 2) =
= 17/5 · 2 =
= 34/5 = 6 4/5 или 6,8