Tính bằng cách thuận tiện nhất :
2/3 × 3/14+1/7×2/3+3/14×2
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\(\frac{1}{2}\cdot\frac{18}{14}+\frac{1}{2}\cdot\frac{3}{14}-\frac{1}{2}\cdot\frac{7}{14}\)
\(=\frac{1}{2}\left(\frac{18}{14}+\frac{3}{14}-\frac{7}{14}\right)\)
\(=\frac{1}{2}\cdot1=\frac{1}{2}\)
a) 145 + 86 + 14 + 55 = ( 145 + 55 ) + (86 + 14 )
= 200 + 100
= 300
b) 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = ( 1+9 +2 + 8) + ( 3 + 7 + 4 + 6 ) + 5
= 20 + 20 + 5
= 45
a,3/5*7/9+11/9*3/5-3/10=3/5*(7/9+11/9)-3/10
=3/5*18/9-3/10
=3/5*2-3/10
=6/5-3/10
=12/10-3/10
=9/10
b,14/13:1/2+3/13*2-2*7/13=14/13*2+3/13*2-2*7/13
=2*(14/13+3/13-7/13)
=2*10/13
=20/13
a/ ( 7/9 + 11/9 ) x 3/5 - 3/10
= 2 x 3/5 - 3/10
= 6/5 - 3/10
= 9/10
b/ 14/13 : 1/2 + 3/13 x 2 - 2 x 7/13
14/13 x 2/1 + 3/13 x 2 - 2 x 7/13
2 x ( 14/13 + 3/13 - 7/13 )
2 x 10/13
20/13
b,14/13:1/2+3/13*2-2*7/13=14/13*2+3/13*2-2*7/13
=2*(14/13+3/13-7/13)
=2*10/13
=20/13
\(\frac{3}{5}\times\frac{6}{7}+\frac{3}{5}:7+\frac{6}{5}\)
\(=\frac{3}{5}\times\frac{6}{7}+\frac{3}{5}\times\frac{1}{7}+\frac{6}{5}\)
\(=\frac{3}{5}\times\left(\frac{6}{7}+\frac{1}{7}\right)+\frac{6}{5}\)
\(=\frac{3}{5}\times1+\frac{6}{5}\)
\(=\frac{3}{5}+\frac{6}{5}=\frac{9}{5}\)
~ Hok tốt ~
\(\frac{29}{12}:\frac{1}{2}-\frac{5}{12}:\frac{1}{2}-\frac{1}{2}\)
\(=\left(\frac{29}{12}-\frac{5}{12}\right):\frac{1}{2}-\frac{1}{2}\)
\(=2:\frac{1}{2}-\frac{1}{2}\)
\(=4-\frac{1}{2}=\frac{7}{2}\)
~ Hok tốt ~
\(\dfrac{3}{7}\cdot\dfrac{9}{26}-\dfrac{1}{14}\cdot\dfrac{1}{13}\)
\(=\dfrac{3\cdot9-1}{14\cdot13}=\dfrac{26}{14\cdot13}=\dfrac{2}{14}=\dfrac{1}{7}\)