bài 1: tính

a) 7/24 + 1/3
ta có: 1/3 = (1 * 8) / (3 * 8) = 8/24
vậy 7/24 + 1/3 = 7/24 + 8/24 = (7 + 8) / 24 = 15/24
rút gọn: 15/24 = (15 / 3) / (24 / 3) = 5/8

b) 21/16 - 5/4
ta có: 5/4 = (5 * 4) / (4 * 4) = 20/16
vậy 21/16 - 5/4 = 21/16 - 20/16 = (21 - 20) / 16 = 1/16

c) 35/32 - 11/16 + 9/8
ta có: 11/16 = (11 * 2) / (16 * 2) = 22/32
9/8 = (9 * 4) / (8 * 4) = 36/32
vậy 35/32 - 11/16 + 9/8 = 35/32 - 22/32 + 36/32 = (35 - 22 + 36) / 32 = (13 + 36) / 32 = 49/32

bài 2: tính

4 + 4/3
ta có: 4 = 4/1 = (4 * 3) / (1 * 3) = 12/3
vậy 4 + 4/3 = 12/3 + 4/3 = (12 + 4) / 3 = 16/3

8 - 8/6
ta có: 8 = 8/1 = (8 * 6) / (1 * 6) = 48/6
vậy 8 - 8/6 = 48/6 - 8/6 = (48 - 8) / 6 = 40/6
rút gọn: 40/6 = (40 / 2) / (6 / 2) = 20/3

9/15 + 2
ta có: 2 = 2/1 = (2 * 15) / (1 * 15) = 30/15
vậy 9/15 + 2 = 9/15 + 30/15 = (9 + 30) / 15 = 39/15
rút gọn: 39/15 = (39 / 3) / (15 / 3) = 13/5

25/12 - 3
ta có: 3 = 3/1 = (3 * 12) / (1 * 12) = 36/12
vậy 25/12 - 3 = 25/12 - 36/12 = (25 - 36) / 12 = -11/12