a) 7/(-25) + (-18/25)+ 4/23 + 5/7 + 19/23
= (-7/25 - 18/25) + (4/23 + 19/23) + 5/7
= -1 + 1 + 5/7
= 0 + 5/7
= 5/7
b) 7/19 . 8/11 + 7/19 . 3/11 + 12/19
= 7/19 . (8/11 + 3/11) + 12/19
= 7/19 . 1 + 12/19
= 7/19 + 12/19
= 1
c) (-25).125.4.(-8).(-17)
= (-25.4).(-125.8).(-17)
= -100.(-1000).(-17)
= 100000.(-17)
= -1700000
d) 7/35 . 10/19 + 7/35 . 9/19 - 2/35
= 7/35 . (10/19 + 9/19) - 2/35
= 7/35 . 1 - 2/35
= 7/35 - 2/35
= 5/35
= 1/7
Đúng 3
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