mng ơi chỉ em với ạ huhu :((

Bài 1 :

a) 1/6 + 2/5 = 5/30 + 12/30 = 17/30

b) 3/5 + -7/4 = 12/20 + -35/20 = -23/20

c) 4/13 + -12/39 = 4/13 + -4/13 = 0

d) -8/18 + -15/27 = -4/9 + -5/9 = -9/9 = -1

Bài 2 :

a) -2/5 + 3/-4 + 6/7 + 3/4 + 2/5

= -2/5 + -3/4 + 6/7 + 3/4 + 2/5

= ( -2/5 + 2/5 ) + ( -3/4 + 3/4 ) + 6/7

= 0 + 0 + 6/7 = 6/7

b) -1/8 + 7/9 + -7/8 + 6/7 + 2/14

= -1/8 + 7/9 + -7/8 + 6/7 + 1/7

= ( -1/8 + -7/8 ) + ( 6/7 + 1/7 ) + 7/9

= -1 + 1 + 7/9 = 7/9

c) 5/11 + 16/22 + -12/4 + -2/11

= 5/11 + 8/11 + (-3) + -2/11

= ( 5/11 + 8/11 + -2/11 ) + (-3)

= 1 + (-3) = -2

d) 7/23 + -10/18 + -4/9 + 16/23

= 7/23 + -5/9 + -4/9 + 16/23

= ( 7/23 + 16/23 ) + ( -5/9 + -4/9 )

= 1 + (-1) = 0