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( x + 1 ) + ( x + 3 ) + ( x + 5 ) + ............. + ( x + 19 ) = 245
( x + x + x + ... + x ) + ( 1 + 3 + 5 + .. + 19 ) = 245
x * 10 + 100 = 245
x * 10 = 245 - 100
x * 10 = 145
x = 145 : 10
x = 14,5
X x 25 - X x 13 = ( 245 : 5 + 150 ) x 3
X x ( 25 - 13 ) = 597
X x 12 = 597
X = 49,75
Vậy x = 49.75
a) \(\dfrac{25}{37}\times\dfrac{18}{29}+\dfrac{18}{29}\times\dfrac{12}{37}\)
\(=\dfrac{18}{29}\times\left(\dfrac{25}{37}+\dfrac{12}{37}\right)\)
\(=\dfrac{18}{29}\times\dfrac{37}{37}\)
\(=\dfrac{18}{29}\times1\)
\(=\dfrac{18}{29}\)
b) \(\dfrac{31}{85}\times\dfrac{11}{19}+\dfrac{31}{85}\times\dfrac{12}{19}-\dfrac{42}{19}\times\dfrac{31}{85}\)
\(=\dfrac{31}{85}\times\left(\dfrac{11}{19}+\dfrac{12}{19}-\dfrac{42}{19}\right)\)
\(=\dfrac{31}{85}\times\dfrac{-19}{19}\)
\(=\dfrac{31}{85}\times-1\)
\(=-\dfrac{31}{85}\)
c) \(\dfrac{16}{53}:\dfrac{17}{9}-\dfrac{16}{53}:\dfrac{17}{8}\)
\(=\dfrac{16}{53}:\left(\dfrac{9}{17}-\dfrac{8}{17}\right)\)
\(=\dfrac{16}{53}:\dfrac{1}{17}\)
\(=\dfrac{16}{901}\)
c) \(\dfrac{1}{5}\times\dfrac{12}{31}\times\dfrac{4}{3}+\dfrac{19}{31}\times\dfrac{4}{15}\)
\(=\dfrac{4}{15}\times\dfrac{12}{31}+\dfrac{19}{31}\times\dfrac{4}{15}\)
\(=\dfrac{4}{15}\times\left(\dfrac{12}{31}+\dfrac{19}{31}\right)\)
\(=\dfrac{4}{15}\times\dfrac{31}{31}\)
\(=\dfrac{4}{15}\times1\)
\(=\dfrac{4}{15}\)
a: =18/29*(25/37+12/37)
=18/29
b: =31/85(11/19+12/19-42/19)
=-31/85
c; =16/53(9/17+8/17)=16/53
d: =4/15(12/31+19/31)=4/15
`a)2019xx85+2019xx25-2019xx10`
`=2019xx(85+25-10)`
`=2019xx100=20190`
__________________________________________________
`b)13/5xx4/9+5/9xx13/9`
`=13/9xx4/5+5/9xx13/9`
`=13/9xx(4/5+5/9)`
`=13/9xx61/45=793/405`
Hoặc:
`b)13/5xx4/9+5/9xx13/5`
`=13/5xx(4/9+5/9)`
`=13/5xx9/9=13/5`
a).(x+x+x+x+...+x)+(1+3+5+....+19)=245
=X x 10+100=245
X x 10=245-100
X x 10=145
x=145:10
x=14,5
( X + 1 ) + ( X + 3 ) + ( X + 5 ) + . . . . . + ( X + 19 ) = 245 |
=> ( X + X + ... + X ) + ( 1 + 3 + ... + 19 ) = 245 ( mỗi nhóm có 10 số hạng )
=> 10 x X + ( 19 + 1 ) x 10 : 2 = 245
=> 10 x X + 100 = 245
=> 10 x X = 245 - 100 = 145
=> X = 145 : 10 = 14,5
Vậy ....................
a) 125 x 45 + 45 x 25 + 90 x 25
=125 x 45 + 45 x 25 + 2 x 45 x 25
=45 x [125 + 25 + ( 2 x 25 )]
=45 x [125 + 25 + 50]
=45 x 200
= 9000
c) 25 x 20 x 4 - 200 x 40
=25 x 2 x 10 x 4 - 200 x 40
=(25 x 2 x 4) x 10 - 200 x 40
=200 x 10 - 200 x 40
=200 x (10 - 40)
=200 x (-30)
= -6000
a)
\(\dfrac{1}{2}=0,5;\dfrac{3}{4}=0,75;\dfrac{7}{5}=1,4;\dfrac{9}{8}=1,125;\dfrac{26}{25}=1,04;\dfrac{120}{125}=0,96\)
b)
\(\dfrac{15}{25}=0,6;\dfrac{75}{25}=3;\dfrac{90}{300}=0,3;\dfrac{27}{36}=0,75;\dfrac{51}{85}=0,6\)
a,1/2=5/10;3/4=75/100;7/5=140/100;26/25=108/100;120/125=960/1000
b,15/25=60/100;75/25=300/100;90/300=3/10;27/36=3/4=75/100;
51/85=3/5=60/100;39/65=3/5=60/100
\(\frac{7}{25}+\frac{18}{25}+\frac{4}{23}+\frac{5}{7}+\frac{19}{23}\)
\(=\left(\frac{7}{25}+\frac{18}{25}\right)+\left(\frac{4}{23}+\frac{19}{23}\right)+\frac{5}{7}\)
\(=1+1+\frac{5}{7}\)
\(=2+\frac{5}{7}=\frac{19}{7}\)