a) 4/63 + 1/18 - (2/5)^2 × 5/7 =
= 2×4/126 + 7/126 - 4/25 × 5/7 =
= 15/126 - 4/35 =
= 5/42 - 4/35 =
= 5×5/210 - 4×6/210 =
= (25-24)/210 =
= 1/210
b) ( 1 + 3/2 × 5/2) : 6 - 1 =
(1 + 15/4) × 1/6 - 1 =
= (4/4 + 15/4) × 1/6 - 1 =
= 19/4 × 1/6 - 1 =
= 19/24 - 1 =
= 19/24 - 24/24 =
= (19-24)/24 =
= - 5/24
