Bạn tham khảo :
-5/30 + -4/12 + 3/21 - 2/4
= -1/6 + -4/12 + 3/21 - 2/4
= -2/12 + -4/12 + 3/21 - 2/4
= -6/12 + 3/21 - 2/4
= -1/2 + 3/21 - 2/4
= -1/2 - 2/4 + 3/21
= -2/4 - 2/4 + 3/21
= -1 + 3/21
= -21/21 + 3/21
= -18/21 = -6/7
b , Không nhìn thấy cả đề
3B ,
-3/5 + -3/7 + 1/3 + -2/5 + 10/7
= ( -3/5 + 1/3 + (-2)/5 ) + ( 3/7 + 10/7)
= ( -9/15 + 5/15 + -6/15) + 13/7
= -10/15 + 13/7
= -2/3 + 13/7
= -14/21 + 39/21
= 25/21
b ,
8/19 + -15/17 + 4/23 - 2/17 + 11/19
= ( 8/19 + 11/19 ) + ( -15/17 - 2/17 ) + 4/23
= 1 + (-1) + 4/23
= 0 + 4/23
= 4/23