a, 25.4:32
b, 34:3.27
c, 42.43:16.22
d, 196:142
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a) (125 - x) + 25 = 98
125 - x = 98 - 25
125 - x = 73
x = 125 - 73
x = 52
b) 100 : (x + 20) = 68 : 34
100 : (x + 20) = 2
x + 20 = 100 : 2
x + 20 = 50
x = 50 - 20
x = 30
c) (3x + 12) . 5 = 25 . 4 - 10
(3x + 12) . 5 = 100 - 10
(3x + 12) . 5 = 90
3x + 12 = 90 : 5
3x + 12 = 18
3x = 18 - 12
3x = 6
x = 6 : 2
x = 3
d) 210 : (2x - 3) - 20 = 10
210 : (2x - 3) = 10 + 20
210 : (2x - 3) = 30
2x - 3 = 210 : 30
2x - 3 = 70
2x = 70 + 3
2x = 73
x = 73/2
a, ( 125 - x ) + 25 = 98
⇒ 125 - x = 73
⇒ x = 52.
Vậy..
b, 100 : ( x + 20 ) = 68 : 34
⇒ 100 : ( x + 20 ) = 2
⇒ x + 20 = 50
⇒ x = 30
Vậy...
c, ( 3 . x + 12 ) . 5 = 25 . 4 - 10
⇒ ( 3 . x + 12 ) . 5 = 90
⇒ 3 .x + 12 = 18
⇒ 3x = 6
⇒ x = 2.
Vậy...
d, 210 : ( 2 .x - 3 ) - 20 = 10
⇒ ( 2 .x - 3 ) - 20 = 21
⇒ 2x - 3 = 41
⇒ 2x = 44
⇒ x = 22.
Vậy..
12.68+34.18-34-142
12.2.34+34.18-34.1-142
=24.34+34.18-34.1-142
=34.(24+18-1)-142
=34.41-142
=1394-142
=1252
1) x - 18 : 3 = 12
x - 6 = 12
x = 12 + 6
x = 18
2) ( x : 3 ) - 18 = 12
x : 3 = 12 + 18
x : 3 = 30
x = 30 x 3
'x = 90
3) ( x - 3 ) : 4 = 7
x - 3 = 7 x 4
x - 3 = 28
x = 28 + 3
x = 31
4 ) ( x : 15 ) - 3 = 25 x 4
( x : 15 ) - 3 = 100
x : 15 = 100 + 3
x : 15 = 103
x = 103 x 15
x = 1545
5) ( x - 25 ) : 9 = 0
x - 25 = 0 x 9
x - 25 = 0
x = 0 + 25
x = 25
6) 34 : ( x - 8 ) = 34
x - 8 = 34 : 34
x - 8 = 1
x = 1 + 8
x = 9
7) ( x + 4 ) x 16 = 80
x + 4 = 80 : 16
x + 4 = 5
x = 5 - 4
x = 1
12. 68 + 34. 18 - 34- 142
=12.2.34+34.18+108
=24.34+34.18+108
=34.(24+18)+108
=34.42+108
=1428+108
=1536
53 + 34 - 142
= 125 + 81 - 196
= 206 - 196
= 10
theo mình nghĩ là thế :))
Bài 2: Tính nhanh
a) 29 + 132 + 237 + 868 + 3
= 29+(132+858)+(237+3)
=29+990+240
=1259
Sửa đề: \(98+99+\dfrac{142}{144}\) \(\rightarrow\dfrac{98}{99}+\dfrac{143}{144}\)
Giải:
\(A=\dfrac{2}{3}+\dfrac{14}{15}+\dfrac{34}{35}+\dfrac{62}{63}+\dfrac{98}{99}+\dfrac{143}{144}+\dfrac{194}{195}\)
\(A=\left(1-\dfrac{1}{3}\right)+\left(1-\dfrac{1}{15}\right)+\left(1-\dfrac{1}{35}\right)+...+\left(1-\dfrac{1}{195}\right)\)
\(A=7-\left(\dfrac{1}{3}+\dfrac{1}{15}+\dfrac{1}{35}+...+\dfrac{1}{195}\right)\)
\(A=7-\left(\dfrac{1}{1.3}+\dfrac{1}{3.5}+\dfrac{1}{5.7}+...+\dfrac{1}{13.15}\right)\)
\(A=7-\left[\dfrac{1}{2}.\left(\dfrac{2}{1.3}+\dfrac{2}{3.5}+\dfrac{2}{5.7}+...+\dfrac{2}{13.15}\right)\right]\)
\(A=7-\left[\dfrac{1}{2}.\left(\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{13}-\dfrac{1}{15}\right)\right]\)
\(A=7-\left[\dfrac{1}{2}.\left(\dfrac{1}{1}-\dfrac{1}{15}\right)\right]\)
\(A=7-\left[\dfrac{1}{2}.\dfrac{14}{15}\right]\)
\(A=7-\dfrac{7}{15}\)
\(A=\dfrac{98}{15}\)
Chúc bạn học tốt!
a) \(64\cdot25+35\cdot25+25=25\cdot\left(64+35+1\right)=2500\)
b) \(92\cdot42+32\cdot8+5\cdot16\)
\(=8\cdot21\cdot23+16\left(16+5\right)\)
\(=8\cdot21\cdot23+16\cdot21\)
\(=8\cdot21\cdot\left(23+2\right)\)
\(=8\cdot21\cdot25\)
\(=2\cdot21\cdot4\cdot25\)
\(=42\cdot100\)
\(=4200\)
c) \(\left(42\cdot43+43\cdot57+43\right)-360:4\)
\(=\left[43\cdot\left(42+57+1\right)\right]-360:4\)
\(=4300-90\)
\(=4210\)
a)4
b)729
c)256
a, 25.4:32
25 . 22 : 25 = 22 = 4
b, 34:3.27
34 . 31 : 33 = 32 = 9
c, 42.43:16.22
24 . 26 . 24 . 22 = 216
d, 196:142
142 : 142 = 1