1 tinh a) -1/16 + -1/24 b) -18/10+0,4 c) -1/8 - 3/20 b) 1/2 - (1/3+1/10) b) 1/2 - -1/3 + 1/23 + 1/6 d) 2/5 + (-4/3) + (-1/2) 2 tim x a) x + 2/3 =4/5 b) x - 2/7 = 7/21 c) 1/20 - (x - 8/5 ) = 1/10 d) 16/5 -x = 4/5 - 3/10 33 tinh nhanh M = 1/2 . 3 + 1/3 . 4 + 1/4 . 5 + ...................+ 1/19 . 20