Đáp án:Bài 3:
a) 3/4 . 16/9 - 7/5 : -21/20
= 4/3 - 7/5 . -20/21
= 4/3 - (-4/3)
= 4/3 + 4/3
= 8/3
b) 2/1/3 - 1/3 . [-3/2 + (2/3 + 0,4 . 5)]
= 7/2 - 1/3 . [-3/2 + (2/3 + 2)]
= 7/2 - 1/3 . [-3/2 + (2/3 + 6/3)]
= 7/2 - 1/3 . [-3/2 + 8/3]
= 7/2 - 1/3 . [-9/6 + 16/6]
= 7/2 - 1/3 . 7/6
= 7/3 - 7/18
= 42/18 - 7/18
= 35/18
c) (20 + 9/1/4) : 2/1/4
= (20 + 37/4) : 9/4
= (80/4 + 37/4) : 9/4
= 117/4 : 9/4
= 117/4 . 4/9
= 13
d) (6- 2/4/5) . 3/1/8 - 1/3/5 : 1/4
= (6 -14/5) . 25/8 - 8/5 : 1/4
= (30/5 - 14/5) . 25/8 - 8/5 . 4/1
= 16/5 . 25/8 - 32/5
= 10 - 32/5
= 50/5 - 32/5
= 18/5
e) 32/15 . (-1/1/5 + 1/1/3)
= 32/15 . (-6/5 + 4/3)
= 32/15 . (-18/15 + 20/15)
= 32/15 . 2/15
= 64/225
g) 0,2 . 15/36 - (2/5 + 2/3) : 1/1/5
= 1/12 - (6/15 + 10/15) : 6/5
= 1/12 - 16/15 . 5/6
= 1/12 - 8/9
= 3/36 - 32/36
= -29/26
h) 1/13/15 . 0,75 - (8/15 + 0.25) . 24/47
= 28/15 . 3/4 - (8/15 + 1/4) . 24/47
= 7/5 - (32/60 + 15/60) . 24/47
= 7/5 - 47/60 . 24/47
= 7/5 - 2/5
= 5/5 = 1
g) 5 . (4/3/4 - 1/25/28) - 1/3/8 : (3/8 + 9/20)
= 5 . (19/4 - 53/28) - 11/8 : (15/40 + 18/40)
= 5 . (133/28 - 53/28) - 11/8 . 40/33
= 5 . 80/28 - 5/3
= 7/4 - 5/3
= 21/12 - 20/12
= 1/12
Bài 4:
a) x : 3/1/15 = 1/1/2
=> x : 46/15 = 3/2
=> x = 3/2 . 46/15
=> x = 23/5
b) 5/4/7 : x = 13
=> 39/7 :x = 13
=> x = 39/7 : 13
=> x = 3/7
h) 2/3.x - 1/2.x = 5/12
=> x.(2/3 - 1/2) = 5/12
=>x.(4/6 - 3/6) = 5/12
=> x . 1/6 = 5/12
=> x = 5/12 : 1/6
=> x = 5/12 . 6
=> x = 5/2
i) 2/1/4.(x - 7/1/3) = 1,5
=> 9/4 . (x - 22/3) = 3/2
=> 9/4.x - 33/2 = 3/2
=> 9/4.x = 3/2 + 33/2
=> 9/4.x = 36/2
=> 9/4.x = 18
=> x = 18 : 9/4
=> x = 18 . 4/9
=> x = 8
Giải thích các bước giải: vì bạn chụp mờ nên có vài chỗ mình nhìn không rõ, nếu có câu nào sai đề bài thì cứ bảo mình nha.
