Đáp án:
Giải thích các bước giải:
a) 2/5+ 3/5 = 5/5 = 1
3/4 + 5/4 = 8/4 = 2
3/8 + 7/8 = 10/8 = 5/4
35/25 + 7/25 = 42/25
b) 2/3 + 3/4 = 8/12 + 9/12 = 17/12
9/4 + 3/5 = 45/20 + 12/20 = 57/20
2/5 + 4/7 = 14/35 + 20/35 = 34/35
3/5 + 4/3 = 9/15 + 20/15 = 29/15
c) 3/12 + 1/4 = 1/4 + 1/4 = 2/4 = 1/2
4/25 + 3/5 = 4/25 + 15/25 = 19/25
26/81 + 4/27 = 26/81 + 12/81 = 38/81
5/64 + 7/8 = 5/64 + 56/64 = 61/64
d) 3 + 2/3 = 9/3 + 2/3 = 11/3
3/4 + 5 = 3/4 + 5/1 = 3/4 + 20/4 = 23/4
12/21 + 2 = 12/21 + 42/21 = 64/21
Bài 2
a) 7/21 + 9/36 = 1/3 + 1/4 = 4/12 + 3/12 = 7/12
b) 12/18 + 21/35 = 1/3 + 21/35 = 35/105 + 63/35 = 98/105
c) 3/21 + 6/42 = 1/7 + 1/7 = 2/7
d) 18/24 + 15/21 = 3/4 + 5/7 = 21/28 + 20/28 = 41/28
Bài 3
a)
x = 1/2 + 3/4
x = 2/4 + 3/4
x = 5/4
b)
x = 5/6 + 19/30
x = 25/30 + 19/30
x = 44/30
Bài 4
a) A = ( 3/4 + 1/4 ) + ( 5/7 + 2/7 ) + 3/5
A = 1 + 1 + 3/5
A = 5/5 + 5/5 + 3/5
A = 13/5
b) B = ( 2/17 + 15/17 ) + ( 15/23 + 8/23 ) + 4/19
B = 1 + 1 + 4/19
B = 19/19 + 19/19 + 4/19
B = 32/19
c) C = ( 3/7 + 4/7 ) + 5/13
C = 1 + 5/13
C = 13/13 + 5/13
C = 18/13
d) D = ( 5/21 + 2/21 ) + 8/24
D = 7/21 + 8/24
D = 1/3 + 1/3
D = 2/3
