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Bài 2:
a, \(\dfrac{5}{23}\) \(\times\) \(\dfrac{17}{26}\) + \(\dfrac{5}{23}\) \(\times\) \(\dfrac{9}{26}\)
= \(\dfrac{5}{23}\) \(\times\) ( \(\dfrac{17}{26}\) + \(\dfrac{9}{26}\))
= \(\dfrac{5}{23}\) \(\times\) \(\dfrac{26}{26}\)
= \(\dfrac{5}{23}\)
b, \(\dfrac{3}{4}\) \(\times\) \(\dfrac{7}{9}\) + \(\dfrac{7}{4}\) \(\times\) \(\dfrac{3}{9}\)
= \(\dfrac{7}{12}\) + \(\dfrac{7}{12}\)
= \(\dfrac{14}{12}\)
= \(\dfrac{7}{6}\)
a)100-9:(372:3.y-1)-14=83
<=>100-9:(124y-1)-14=83
<=>86-9:(124y-1)=83
<=>9:(124y-1)=3
<=>124y-1=3
<=>124y=4
<=>y=\(\frac{1}{31}\approx0,3223\)
b)7260-120:24.y+924=528,3
<=>8184-5y=528,3
<=>5y=7655,7
<=>y=1531,14
c)2000-52:(615:3:y-15)-14=1984
<=>1986-52:(205:y-15)=1984
<=>52:(205:y-15)=2
<=>205:y-15=26
<=>205:y=41
<=>y=5
d)y+y.1/3+5/18=7/18
<=>4/3y=1/9
<=>y=1/12
e)13/15-(5/21+y)7/12=7/10
<=>7/12.(5/21+y)=1/6
<=>5/36+7/12y=1/6
<=>7/12y=1/36
<=>y=1/21\(\approx\)0,4762
h)y+2.y+3.y+...+10.y=49,5
<=>55y=49,5
<=>y=0,9
i)y.(1975/8.9+1885/9.10+1755/10.11+1579/11.12)=1/24
<=>7991,364899y=1/24
<=>y=33/6329161
tích nha mỏi tay quá
\(\frac{x}{27}-\frac{2}{9}=\frac{6}{18}\)
\(\frac{x}{27}=\frac{6}{18}-\frac{2}{9}\)
\(\frac{x}{27}=\frac{3}{9}-\frac{2}{9}\)
\(\frac{x}{27}=\frac{1}{9}\)
\(\frac{x}{27}=\frac{3}{27}\)
\(x=3\)
Ấy nhầm, làm lại nha:
\(\frac{x}{27}-\frac{2}{9}=\frac{6}{18}\)
\(\frac{x}{27}=\frac{6}{18}+\frac{2}{9}\)
\(\frac{x}{27}=\frac{3}{9}+\frac{2}{9}\)
\(\frac{x}{27}=\frac{5}{9}\)
\(\frac{x}{27}=\frac{15}{27}\)
\(x=15\)
a)\(\frac{x}{17}=\frac{60}{204}=\frac{5}{17}\Rightarrow x=5\)
b)\(\frac{6+x}{33}=\frac{7}{11}\Rightarrow11\left(6+x\right)=7.33\Rightarrow11.6+11x=231\Rightarrow66+11x=231\)
\(\Rightarrow11x=231-66\Rightarrow11x=165\Rightarrow x=\frac{165}{11}=15\)
c)\(\frac{12+x}{43-x}=\frac{2}{3}\Rightarrow2\left(43-x\right)=3\left(12+x\right)\Rightarrow2.43-2x=3.12+3x\)
\(86-2x=36+3x\Rightarrow86-36=3x+2x\Rightarrow50=5x\Rightarrow x=\frac{50}{5}=10\)
Ta có:
A = 1 + 3 + 5 + 7 +... + 101
A = \(\frac{102.51}{2}=2601\)
M = 16 - 18 + 20 - 22 + 24 - 26 + .. + 64 - 66 + 68
M = ( 16 - 18 ) + ( 20 - 22 ) + ( 24 - 26 ) + ... + ( 64 - 66 ) + 68
M = (- 2 + - 2 + -2 + ... + - 2 ) + 68
M = 25/2 . ( - 2 ) + 68
M = -25 + 68
M = 43
H = ( 1 + 2 + 3 +...+ 99 ) x ( 13 x 15 - 12 x 15 - 15 )
H = ( 1 + 2 + 3 +...+ 99 ) x { (13 - 12 - 1) x 15 }
H = ( 1 + 2 + 3 +...+ 99 ) x 0
H = 0
G = 1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + 9 + 10 - 11 - 12 + 13 + 14 - ... + 301 + 302
G = ( 1 + 2 ) + ( -3 - 4 ) + ( 5 + 6 ) + ( -7 - 8 ) + ( 9 + 10 ) + ( - 11 - 12 ) + ( 13 + 14 ) -...+ ( 301 + 302 )
G = ( 3 - 7 ) + ( 11 - 15 ) + ( 19 - 23 ) + 27 - ... + 603
G = -4 + - 4 + -4 + 27 - ... + 603
G = 75 x ( -4 ) + 603
G = -300 + 603
G = 303
2.
a) 1 + 2 + 3 + 4 +...+ 99 + 100 + 2 x X = 5052
= > \(\frac{100.101}{2}\)+ 2 x X = 5052
= > 5050 + 2 x X = 5052
= > 2X = 2
= > X = 1
a) X = 15
b) X = 4
c ) X= 23
d) X= 11
( Chỉ là ý kiến riêng thôi nhé, nhận gạch đá )
a) \(\frac{6+x}{33}=\frac{7}{11}\)
=> (6 + x). 11 = 33.7
=> 66 + 11x = 231
=> 11x = 231 - 66
=> 11x = 165
=> x = 165 : 11
=> x = 15
b) 15/26 + x/13 = 46/52
=> x/13 = 23/26 - 15/26
=> x/13 = 4/13
=> x = 4
c) 121/27 x 54/11 < x < 100/21 : 25/126
=> 22 < x < 24
=> x = 23 (vì x là số tự nhiên)
d) 1 < 11/x < 12
=> 11/x \(\in\){2; 3; 4 ; ...; 11}
=> x \(\in\) {11/2; 11/3; ...; 1}
Vì x là số tự nhiên => x = 1