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a\Câu 1:
200 : ( 15 - x ) = 15 + 5
200 : ( 15 - x ) = 20
15 - x = 200 : 20
15 - x = 10
x = 15 - 10
x = 5
Câu 2:
63 : ( x - 5 ) = 22 -1
63 : ( x - 5 ) = 21
x - 5 = 63 : 21
x - 5 = 3
x = 3 + 5
x = 8
3 x 15 + 21 x 15 + 85 x 5
= 45 + 315 + 425
= 785
15 - 30 + 40
= 25
21 + 19 - 50 + 10
= 0
\(\dfrac{1}{5}-\dfrac{1}{4}+2\)
\(=-\dfrac{1}{20}+2\)
\(=\dfrac{39}{20}\)
\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)
\(=\dfrac{5}{12}\times\dfrac{1}{4}\)
\(=\dfrac{5}{12}\times\dfrac{3}{12}\)
\(=\dfrac{5}{48}\)
\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)
\(=-\dfrac{9}{20}\)
\(3\times15+21\times15+85\times5\\ =15\times\left(3+21\right)+425\\ =15\times24+425\\ =360+425\\ =785\)
\(15-30+40\\ =\left(15+40\right)-30\\ =55-30\\ =25\)
\(21+19-50+10\\ =\left(21+19\right)-\left(50-10\right)\\ =40-40\\ =0\)
\(\dfrac{1}{5}-\dfrac{1}{4}+2\)
\(=\dfrac{4}{20}-\dfrac{5}{20}+\dfrac{40}{20}\)
\(=\dfrac{\left(4+40\right)}{20}-\dfrac{5}{20}\)
\(=\dfrac{44}{20}-\dfrac{5}{20}\)
\(=\dfrac{39}{20}\)
\(\left(\dfrac{1}{4}+\dfrac{1}{6}\right)\times\left(\dfrac{1}{2}-\dfrac{1}{4}\right)\)
\(=\dfrac{5}{12}\times\dfrac{1}{4}\)
\(=\dfrac{5}{48}\)
\(\dfrac{1}{10}+\dfrac{1}{5}-\dfrac{3}{4}\)
\(=\dfrac{2}{20}+\dfrac{4}{20}-\dfrac{15}{20}\)
\(=\dfrac{6}{20}-\dfrac{15}{20}\)
\(=-\dfrac{9}{20}\)
b)0,5x+2/3x+2/3=7/2
1/2x+2/3x+2/3=7/2
x(1/2+2/3)+2/3=7/12
x.7/6+2/3 =7/12
x.7/6 =7/12-2/3
x.7/6 =-1/12
x =-1/12:7/6
x =-1/14
b)3/5-2/15:x=1/2
2/15:x =3/5-1/2
2/15:x =1/10
x =2/15:1/10
x = 4/3
a) \(15-3\left(x-1\right)-x=20\)
\(15-3x+3-x=20\)
\(-4x=2\)
\(x=-\frac{1}{2}\)
b) \(6x-2\left(x+3\right)=10\)
\(6x-2x-6=10\)
\(4x=16\)
\(x=4\)
c) \(25:\left(x+4\right)=5\)
\(x+4=25:5=5\)
\(x=1\)
d tự làm nha!
\(x\) \(\times\) \(\dfrac{4}{5}\) = 15
\(x\) = 15 : \(\dfrac{4}{5}\)
\(x\) = \(\dfrac{75}{4}\)
\(\dfrac{12}{25}\) \(\times\) \(x\) = \(\dfrac{4}{10}\)
\(x\) = \(\dfrac{4}{10}\) : \(\dfrac{12}{25}\)
\(x\) = \(\dfrac{5}{6}\)
123,45 + 23,56 +76,44 + 54,55
= (123,45 + 54,55) + (23,56 + 76,44)
= 178 + 100
= 278
456 x 45 + 456 x 10 + - 456 x 55
=456 x (45 +10-55)
=456 x 0
=0
2,5 x 8,5 + 7,5 x 8,5
=8,5 x (2,5 +7,5)
= 8,5 x 10
= 85
86 x 5 + 86 x 4 + 86
= 86 x (5+4+1)
= 86 x10
860
a, 2x3x4x8x25x125= (2x3)x(4x25)x(8x125)= 6x100x1000=600000
b,42/5 +56/9+23/4+3/5+1/3+1/4= (42/5+3/5)+(23/4+1/4)+(56/9+1/3)=9+6+59/9=
= 1.2.3.(1+2+5) / 2.3.5.(1+2+5)
= 1.2.3/2.3.5 = 1/5