g, 12 . 41 + 3 . 20 . 4 + 2 . 39 . 6
= 12 . 41 + 12 .20 + 12 . 39
= 12 . (41 + 20 + 39)
= 12 . 100
= 1200
i, 85 . (35 - 27) - 35 . (85 - 27)
= 85 . 35 - 85 . 27 - 85 . 35 + 35 . 27
= (85 . 35 - 85 . 35) - (85 . 27 - 35 . 27)
= 0 - [27 . (85 - 35)]
= 0 - [27 . 50]
= 0 - 1350
= -1350
k, 11 + 12 + 13 + ... + 50
= (11 + 50) + (12 + 49) + ... + (30+31) (20 nhóm)
= 61 + 61 + ... + 61 (20 nhóm)
=61 . 20
= 1220
Học tốt~~