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a.35 x 34 + 35 x 38 + 65 x 75 + 45 x 65
= 35 x (34 + 38) + 65 x 75 + 65 x 45
= 35 x 72 + 65 x (75+45)
= 35 x 72 + 65 x 120
= 35 x 72 + 65 x (72 + 48)
= 35 x 72 + 65 x 72 + 65 x 48
= (35+65) x 72 + 65 x 48
= 100 x 72 + 65 x 48
= 7200 + 3120
= 10320
b.39 x 8 + 60 x 2 + 21 x 8
=39 x 8 + 15 x 4 x 2 +21 x 8
= 39 x 8 + 15 x 8 + 21 x 8
=(39 + 15 + 21) x 8
= 75 x 8
= 600
c.58 x 75 + 58 x 50 - 58 + 25
= 58 x 75 + 58 x 50 - 58 x 1 + 25
= 58 x(75+50-1)+25
= 58 x 124 + 25
= 7192 + 25
= 7217
d.125 x 98 - 125 x 46 - 52 x 25
= 25 x 5 x 98 - 25 x 5 x 46 - 25 x 52
= 25 x 490 - 25 x 230 - 25 x 52
= 25 x (490 - 230 - 52)
= 25 x 208
= 5200
a) thay a = 119 ;b = 0 vào bt : ( 119 x a +2005 ) +119 :a- b x 2005 ta có :
( 119 x 199+2005) +119 :119 -0 x2005
<=> (14161+2005 ) +119 : 119 -0 x 2005
<=>16166+119 : 199 -0 x 2005
<=> 16166+1 - 0 x 2005
<=> 16166 +1 - 0
<=> 16167
b) 100 : {2 x [ 52-(25 - 8 )]}
<=> 100 : { 2 x [ 52 - 17] }
<=> 100 : { 2 x 35 }
<=> 100 : 70
<=> \(\frac{10}{7}\)
c) 12 : { 390 : [ 500 - ( 125 +25 : 7 ) ] }
<=> 12 : { 390 : [ 500 - ( \(\frac{900}{7}\) ) ] }
<=> 12 : { 390 : [ \(\frac{2600}{7}\) ] }
<=> 12 : { \(\frac{21}{20}\) }
<=> \(\frac{80}{7}\)
a. 5 * x * 8,3 = 20,75
=> 41,5 * x = 20,75
=> x = 20,75 : 41,5
=> x = 0,5
b. 5,75 + x * 1,25 = 8 + 1/4
=> 5,75 + x * 1,25 = 8,25
=> x * 1,25 = 8,25 - 5,75
=> x * 1,25 = 2,5
=> x = 2,5 : 1,25
=> x = 2
a. 5 * x * 8,3 = 20,75
=> 41,5 * x = 20,75
=> x = 20,75 : 41,5
=> x = 0,5
b. 5,75 + x * 1,25 = 8 + 1/4
=> 5,75 + x * 1,25 = 8,25
=> x * 1,25 = 8,25 - 5,75
=> x * 1,25 = 2,5
=> x = 2,5 : 1,25
=> x = 2
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) \(\dfrac{12}{7}\div x+\dfrac{2}{3}=\dfrac{7}{5}\)
\(\dfrac{12}{7}\div x=\dfrac{7}{5}-\dfrac{2}{3}\)
\(\dfrac{12}{7}\div x=\dfrac{11}{15}\)
\(x=\dfrac{12}{7}\div\dfrac{11}{15}\)
\(x=\dfrac{180}{77}\)
Tính
a) 60 : 8 x 2,6
=7,5x 2,6
=19,5
b) 480 : 125 : 4
=3,84:4.
=0,96
c) ( 75 + 45 ) : 75
=120:75
=1,6
d) 2001 : 25 - 1999 :25
=25: ( 2001-1999)
=12,5
