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\(\dfrac{45.21.25}{7.15.36}=\dfrac{3.3.3.5.7.5.5}{7.5.3.3.2.3.2}=\dfrac{25}{4}\)
45\7 x 21\15 x 25/36
=45x21x25/7x15x36
=15x3x7x3x25/7x15x3x12
=3x25/12
=75/12
=25/4
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![](https://rs.olm.vn/images/avt/0.png?1311)
9 x 4 x 198 - 6 x 18 x 17 - 36 x 47
= 36 x 198 - 36 x 51 - 36 x 47
= 36 x (198 - 51 - 47)
= 36 x 100
= 3600
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Ta thấy: 8 x 9=72; 6 x 12=72; 4 x 18=72; 2 x 36=72.
Sử dụng tính chất phân phối của phép nhân với phép cộng.
Ta có: 72 x(10 + 25 + 66) - 72
= 72 x 101 - 72
= 7272 - 72
= 7200.
☘nat
![](https://rs.olm.vn/images/avt/0.png?1311)
A = 8 x 9 x 10 + 6 x 25 x 12 + 4 x 18 x 66 - 2 x 36
A = (8 x 9) x 10 + (6 x 12) x 25 + (4 x 18) x 66 - 2 x 36
A = 72 x 10 + 72 x 25 + 72 x 66 - 72
A = 72 x ( 10 + 25 + 66 - 1)
A = 72 x 100
A = 7200
![](https://rs.olm.vn/images/avt/0.png?1311)
a)
= 25 x 4 x 7 x 9
= 100 x 63
= 6300
b)
= 2 x 50 x 47 x 10
= 100 x 470
= 47000
c)
= 20 x 5 x 9 x 6
= 100 x 54
= 5400
![](https://rs.olm.vn/images/avt/0.png?1311)
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) \(\dfrac{12}{7}\div x+\dfrac{2}{3}=\dfrac{7}{5}\)
\(\dfrac{12}{7}\div x=\dfrac{7}{5}-\dfrac{2}{3}\)
\(\dfrac{12}{7}\div x=\dfrac{11}{15}\)
\(x=\dfrac{12}{7}\div\dfrac{11}{15}\)
\(x=\dfrac{180}{77}\)
18 x 25 + 36 x 36 + 6 x 9
= 18 x 25 + 18 x 2 x 36 + 6 x 3 x 3
= 18 x 25 + 18 x 72 + 18 x 3
= 18 x ( 25 + 72 + 3 )
= 18 x 100
= 1800
= 450+1296+54
=1800