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chuyển đổi lại : (7x - 3) : 12 = 13
=> (7x - 3) = 13 * 12
=> 7x - 3 = 156
=> 7x = 159
=> x= 159/7
[(7x - 31) : 5] * 36 = 7236
=> [(7x - 31) : 5] = 7236 : 36 = 201
=> (7x - 31) : 5 = 201
=> 7x - 31 = 1005
=> 7x = 1036
=> x = 148
1 + 2 + 3 + 4 + 5 +... + 100 + x = 5350
SSH : \(\left(100-1\right):1+1=100\)
=> tổng : \(\frac{\left(1+100\right)\cdot100}{2}=5050\)
=> 5050 + x = 5350
=> x = 5350 - 5050 = 300
80 - 9(x - 4) = 35
=> 9(x - 4) = 80 - 35 = 45
=> x - 4 = 45 : 9
=> x - 4 = 5
=> x = 9
(3x - 21) : 4 + 108 = 114
=> (3x - 21) : 4 = 114 - 108 = 6
=> 3x - 21 = 24
=> 3x = 45
=> x = 15
[(6x - 72) : 2 - 84]*14 = 2814
=> [(6x - 72) : 2 - 84] = 201
=> (6x - 72) : 2 - 84 = 201
=> (6x - 72) : 2 = 285
=> 6x - 72 = 570
=> 6x = 642
=> x = 107
28x + 12x = 80
=> 40x = 80
=> x = 2
249 - 7(1 + x) = 200
=> 7(1 + x) = 49
=> 1 + x = 7
=> x = 6
20 - [(x - 5) * 7 + 4] = 2
=> [(x - 5) * 7 + 4] = 18
=> (x - 5)*7 + 4 = 18
=> (x - 5) * 7 = 14
=> x - 5 = 2
=> x = 7
\(\frac{7x-33}{12}=13\)
\(7x-33=13\cdot12\)
\(7x-33=156\)
\(7x=156+33\)
\(7x=189\)
\(x=\frac{189}{7}=27\)
\(\frac{7x-31}{5}\cdot36=7236\)
\(\frac{7x-31}{5}=\frac{7236}{36}\)
\(\frac{7x-31}{5}=201\)
\(7x-31=201\cdot5\)
\(7x-31=1005\)
\(7x=1005+31\)
\(7x=1036\)
\(x=\frac{1036}{7}=148\)
\(1+2+3+4+5+..+100+x=5350\)
\(\left(1+2+3+4+5+...+100\right)+x=5350\)
Phần 1 + 2 + 3 + 4 + 5 + ... + 100 có số số hạng là :
\(\frac{100-1}{1}+1=100\) ( số hạng )
\(\Rightarrow\frac{\left(100+1\right)\cdot100}{2}+x=5350\)
\(5050+x=5350\)
\(x=5350-5050=300\)
\(80-9\left(x-4\right)=35\)
\(9\left(x-4\right)=80-35\)
\(9\left(x-4\right)=45\)
\(x-4=\frac{45}{9}\)
\(x-4=5\)
\(x=5+4=9\)
\(\frac{3x-21}{4}+108=114\)
\(\frac{3x-21}{4}=114-108\)
\(\frac{3x-21}{4}=6\)
\(3x-21=6\cdot4\)
\(3x-21=24\)
\(3x=24+21\)
\(3x=45\)
\(x=\frac{45}{3}=15\)
\(14\left(\frac{6x-72}{2}-84\right)=2814\)
\(3x-36-84=\frac{2814}{14}\)
\(3x-120=201\)
\(3x=201+120\)
\(3x=321\)
\(x=\frac{321}{3}=107\)
\(28x+12x=80\)
\(x\left(28+12\right)=80\)
\(x\cdot40=80\)
\(x=\frac{80}{40}=2\)
\(249-7\left(1+x\right)=200\)
\(-7\left(1+x\right)=200-249\)
\(-7\left(1+x\right)=-49\)
\(1+x=\frac{-49}{-7}\)
\(1+x=7\)
\(x=7-1=6\)
\(20-7\left(x-5\right)+4=2\)
\(20-7\left(x-5\right)=2-4\)
\(20-7\left(x-5\right)=-2\)
\(-7\left(x-5\right)=-2-20\)
\(-7\left(x-5\right)=-22\)
\(x-5=\frac{-22}{-7}\)
\(x=\frac{22}{7}+5=\frac{57}{7}\)
Bài 1
a) \(5\times72\times10\times2=\left(5\times2\times10\right)\times72=100\times72=7200\)
b) \(40\times125=5\times\left(8\times125\right)=5\times1000=5000\)
c) \(16\times6\times25=4\times4\times6\times25=\left(4\times6\right)\times\left(4\times25\right)=24\times100=2400\) Bài 2:
a) \(24\times57+43\times24=24\times\left(57+43\right)=24\times100=2400\)
b) \(12\times19+80\times12+12=12\times\left(19+80+1\right)=12\times100=1200\)
c) \(\left(36\times15\times169\right)\div\left(5\times18\times13\right)\)
\(=\left(18\times2\times3\times5\times13\times13\right)\div\left(5\times18\times13\right)\)
\(=\left(2\times3\times13\right)\times\left(18\times5\times13\right)\div\left(5\times18\times13\right)\)
\(=2\times3\times13\)
\(=78\)
d) \(\left(44\times52\times60\right)\div\left(11\times13\times15\right)\)
\(=\left(4\times11\times4\times13\times4\times15\right)\div\left(11\times13\times15\right)\)
\(=\left(4\times4\times4\right)\times\left(11\times13\times15\right)\div\left(11\times13\times15\right)\)
\(=4\times4\times4\)
\(=64\)
Bài 3:
a) \(x-280\div35=5\times54\)
\(x-8=270\)
\(x=270+8\)
\(x=278\)
b) \(\left(x-280\right)\div35=54\div4\)
\(\left(x-280\right)\div35=\dfrac{27}{2}\)
\(x-280=\dfrac{27}{2}\times35\)
\(x-280=\dfrac{945}{2}\)
\(x=\dfrac{945}{2}+280\)
\(x=\dfrac{1505}{2}\)
c) \(\left(x-128+20\right)\div192=0\)
\(x-128+20=0\times192\)
\(x-128+20=0\)
\(x-128=0-20\)
\(x-128=-20\)
\(x=-20+128\)
\(x=108\)
d) \(4\times\left(x+200\right)=460+85\times4\)
\(4\times\left(x+200\right)=460+340\)
\(4\times\left(x+200\right)=800\)
\(x+200=800\div4\)
\(x+200=200\)
\(x=200-200\)
\(x=0\)
Bài 4:
a) \(\dfrac{7}{12}-\dfrac{5}{12}=\dfrac{2}{12}=\dfrac{1}{6}\)
b) \(\dfrac{8}{11}+\dfrac{19}{11}=\dfrac{27}{11}\)
c) \(\dfrac{3}{8}+\dfrac{5}{12}=\dfrac{9}{24}+\dfrac{10}{24}=\dfrac{19}{24}\)
d) \(\dfrac{3}{4}+\dfrac{7}{12}=\dfrac{9}{12}+\dfrac{7}{12}=\dfrac{16}{12}=\dfrac{4}{3}\)
Bài 5:
a) \(x-\dfrac{6}{7}=\dfrac{5}{2}\)
\(x=\dfrac{5}{2}+\dfrac{6}{7}\)
\(x=\dfrac{47}{14}\)
b) \(\dfrac{12}{7}\div x+\dfrac{2}{3}=\dfrac{7}{5}\)
\(\dfrac{12}{7}\div x=\dfrac{7}{5}-\dfrac{2}{3}\)
\(\dfrac{12}{7}\div x=\dfrac{11}{15}\)
\(x=\dfrac{12}{7}\div\dfrac{11}{15}\)
\(x=\dfrac{180}{77}\)
Bài 1:
a) 2/19 + 2/10 + 2/22 + 17/19 + 2/11 + 4/5 + 8/11
=(2/19 +17/19) + 1/5 + 1/11 + 2/11 + 4/5 + 8/11
= 1 + (1/5 + 4/5) + (2/11 + 8/11 + 1/11)
= 1 + 1 + 1 = 3
b) 3/9 + 4/12 + 6/18 + 1/3 + 5/15 + 7/21
= 1/3 + 1/3 + 1/3 + 1/3 + 1/3 + 1/3
= 1/3 x 6 = 2
c) 100 + (125x3-125x2-125) x (1 + 3 + 5 + 7 + ...+ 97 + 99)
= 100 + [125x(3-2-1)] x A
= 100 + (125x0) x A
= 100 + 0 x A
= 100 + 0
= 100
Bài 2:
Gọi số đó là ab
(a+b) x 6 = ab
a x 6 + b x 6= a x 10 + b
b x 5 = a x 4
suy ra a=5; b=4; ab=54
Bài 3:
Vì các số lẻ x 5 đều có tận cùng là 5 nên các tích đều có tận cùng là 5.
Mà 5x3=15 nên P có tận cùng là 5
Bài 1:
a) 2/19 + 2/10 + 2/22 + 17/19 + 2/11 + 4/5 + 8/11
=(2/19 +17/19) + 1/5 + 1/11 + 2/11 + 4/5 + 8/11
= 1 + (1/5 + 4/5) + (2/11 + 8/11 + 1/11)
= 1 + 1 + 1 = 3
b) 3/9 + 4/12 + 6/18 + 1/3 + 5/15 + 7/21
= 1/3 + 1/3 + 1/3 + 1/3 + 1/3 + 1/3
= 1/3 x 6 = 2
c) 100 + (125x3-125x2-125) x (1 + 3 + 5 + 7 + ...+ 97 + 99)
= 100 + [125x(3-2-1)] x A
= 100 + (125x0) x A
= 100 + 0 x A
= 100 + 0
= 100
Bài 2:
Gọi số đó là ab
(a+b) x 6 = ab
a x 6 + b x 6= a x 10 + b
b x 5 = a x 4
suy ra a=5; b=4; ab=54
Bài 3:
Vì các số lẻ x 5 đều có tận cùng là 5 nên các tích đều có tận cùng là 5.
Mà 5x3=15 nên P có tận cùng là 5
`@` `\text {Ans}`
`\downarrow`
`1,`
`a)`
`5 \times 72 \times 10 \times 2`
`= 5 \times 2 \times 10 \times 72`
`= 10 \times 10 \times 72`
`= 100 \times 72`
`= 7200`
`b)`
`40 \times 125`
`= 4 \times 10 \times 25 \times 5`
`= (5 \times 10) \times (4 \times 25)`
`= 50 \times 100`
`= 5000`
`c)`
`4 \times 2021 \times 25`
`= (4 \times 25) \times 2021`
`= 100 \times 2021`
`= 202100`
`d)`
`16 \times 6 \times 25`
`= 4 \times 4 \times 6 \times 25`
`= (4 \times 25) \times 4 \times 6`
`= 100 \times 24`
`= 2400`
`2,`
`a)`
`24 \times 57 + 43 \times 24`
`= 24 \times (57+43)`
`= 24 \times 100`
`= 2400`
`b)`
`12 \times 19 + 80 \times 12 +12`
`= 12 \times (19 + 80 + 1)`
`= 12 \times 100`
`= 1200`
`c)`
`(36 \times 15 \times 169) \div (5 \times 18 \times 13)`
`= 36 \times 15 \times 169 \div 5 \div 18 \div 13`
`= 6 \times 6 \times 3 \times 5 \times 13 \times 13 \div 5 \div 3 \times 6 \div 13`
`= (6 \div 6) \times (3 \div 3) \times (5 \div 5) \times (13 \div 13) \times 6 \times 13`
`= 6 \times 13`
`= 78`
`d)`
`(44 \times 52 \times 60) \div ( 11 \times 13 \times 15)`
`= 44 \times 52 \times 60 \div 11 \div 13 \div 15`
`= 4 \times 11 \times 13 \times 4 \times 15 \times 4 \div 11 \div 13 \div 15`
`= (11 \div 11) \times (13 \div 13) \times (15 \div 15) \times 4 \times 4 \times`
`= 4 \times 4 \times 4`
`= 64`
`3,`
`a)`
`x - 280 \div 35 = 5 \times 54`
`x - 8 = 270`
`x = 270 + 8`
`x = 278`
`b)`
`(x - 280) \div 35 = 54 \div 4`
`(x - 280) \div 35 = 13,5`
`x - 280 = 13,5 \times 35`
`x - 280 = 472,5`
`x = 472,5 + 280`
`x = 752,5`
`c)`
`(x - 128 + 20) \div 192 = 0`
`x - 128 + 20 = 0 \times 192`
`x - 128 + 20 = 0`
`x - 108 = 0`
`x = 0 + 108`
`x = 108`
`d)`
`4 \times (x + 200) = 460 + 85 \times 4`
`4 \times (x+200) = 460 + 340`
`4 \times (x+200) = 800`
`x + 200 = 800 \div 4`
`x + 200 = 200`
`x = 200 - 200`
`x = 0`
`4,`
`a)`
`7/12 - 5/12`
`= (7 - 5)/12`
`= 2/12`
`= 1/6`
`b)`
`8/11 + 19/11`
`= (8+19)/11`
`= 27/11`
`c)`
`3/8 + 5/12`
`= 9/24 + 10/24`
`= 19/24`
`d)`
`3/4 + 7/12`
`= 9/12 + 7/12`
`= 16/12`
`= 4/3`
`5,`
`a)`
`x - 6/7 = 5/2`
`x = 5/2 + 6/7`
`x = 47/14`
`b)`
`12/7 \div x + 2/3 = 7/5`
`12/7 \div x = 7/5 - 2/3`
`12/7 \div x = 11/15`
`x = 12/7 \div 11/15`
`x = 180/77`
`@` `\text {Kaizuu lv uuu}`
(2600+6400)-3x=1200
10 000-3x=1200
3x=9000-1200
3x=7 800
x=7800/3
x=2600
Bài 1:
a) x - 32 + 25 = 12 x 2
x- 32 +25 = 24
x -32 = -1
x = 31
b) 24 + x - 3 = 21
24+x = 24
x = 0
c) x * 10 : 2 = 40
x *10 = 80
x = 8
Bài 2:
a) 123 - 82 x 6= 123- 492= -369
b) 458 - 125 + 23= 333+23 = 356
c) 325 + 125 x 125 x 325= 325 + 5 078 450
Cái này giống như bài lớp 6 ý.
Bài 1 : Tìm x
a) x - 32 + 25 = 12 x 2
x - 32 + 25 = 24
x - 32 = 24 - 25
x - 32 = ( - 1 )
x = ( -1 ) + 32
x = 31
b) 24 + x - 3 = 21
24 + x = 21 + 3
24 + x = 24
x = 24 - 24
x = 0
c) x * 10 : 2 = 40
x * 10 = 40 x 2
x * 10 = 80
x = 80 : 10
x = 8
Bài 2: Tính giá trị của biểu thức
a) 123 - 82 x 6
123 - 492
-369
b) 458 - 125 + 23
333 + 23
356
c) 325 + 125 x 125 x 325
325 + 5078125
5078450
a/ 440 + 2 [ 125 - x ] = 546
==> 2 [ 125 - x ] = 546 - 440
==> 2 [ 125 - x ] 106
==> 125 - x = 106 : 2
==> 125 - x = 53 ==> x = 125 - 53 =72
b/ 7x - 33 = 27 : 24
==> 7x - 27 = 27-4 = 23 = 8
==> 7x = 8+ 27
==> 7x = 35 ==> x = 35 : 7 = 5
c/ [ 12x - 43 ] . 83 = 4 . 84
==> [ 12x - 26 ] . 29 = 22 . 212
==> [ 12x - 26 ] . 29 = 214
==> [ 12x - 26 ] = 214 : 29 = 25
==>. 12x = 25 + 26 = 96
==> x = 96 : 12 = 8
d/ 123 - 5. [ x + 4 ] = 38
==> 5. [ x + 4 ] = 123 - 38
==> 5. [ x + 4 ] = 85
==> x + 4 = 85 : 5
==> x + 4 = 17
==> x = 17 - 4 = 13
e/ [ 2600 + 6400 ] - 3.x = 1200
==> 9000 - 3x = 1200
==> 3x = 9000 -1200 = 7800
==> x = 7800 : 3 = 2600
f/ x2 - 72 : 36 = 23
==> x2 - 2 = 23
==> x2 = 23 + 2
==>x2 = 25
==> x2 = 52
==> x = 5