a, -5/8 - ( -1/7 ) + 5/8 c, -3/7 . 2/11 + -3/7 . 9/11 + 1 và 3/7
-5/8 + 5/8 - ( -1/7 ) = -3/7. ( 2/11 + 9/11 ) + 10/7
0 - ( -1/7 ) = -1/7 = -3/7. 11/11 + 10/7
b, ( 4/5 - 1/20 ) : 1/4 = -3/7 .1 + 10/7
= 15/20 : 1/4 = -3/7 + 10/7
= 15/20 . 4/1 = 7/7 = 1
= 15/5 = 3