A = 1/3 - 1/3 × 4/7
A = 1/3 - 4/21
A = 1×7/3×7 - 4/21
A = 7/21 - 4/21
A = 3/21
A = 1×3/3×7
A = 1/7
B = 6/5 + (1/15 - 1/5)
B = 6/5 + (1/15 - 1×3/5×3)
B = 6/5 + (1/15 - 3/15)
B = 6/5 + (-2/15)
B = 6×3/5×3 - 2/15
B = 18/15 - 2/15
B = 16/15
B = 1,06...
