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a, 1+2+3+4+5+6+7+8+9
= (1+9)+(2+8)+(3+7)+(4+6)+5
= 10+10+10+10+5 = 45
b, 1,1+2,2+3,3+4,4+5,5+6,6+7,7+8,8+9,9
= (1,1+9,9)+(2,2+8,8)+(3,3+7,7)+(4,4+6,6)+5,5
= 11+11+11+11+5,5
= 11*4 + 5,5
= 44+5,5 = 49,5
1+2+3+4+5+6+7+8+9=45
1,1+2,2+3,3+4,4+5,5+6,6+7,7+8,8+9,9=49,5
a,3,25+0,9-x=0,97
4,15-x=0,97
x=4,15-0,97
x=3,18
b,4,4-9,2+x=1,2
-4,8+x=1,2
x=1,2-(-4,8)
x=6
c,7/5+x-2/5=4
7/5+x=4+2/5
7/5+x=22/5
x=22/5-7/5
x=15/5
x=3
d,1 3/4+x-7/8=5
7/4+x-7/8=5
7/4+x=5+7/8
7/4+x=47/8
x=47/8-7/4
x=47/8-14/8
x=33/8
a,3,25+0,9-x=0,97
4,15-x=0,97
x=4,15-0,97
x=3,18
b,4,4-9,2+x=1,2
-4,8+x=1,2
x=1,2-(-4,8)
x=6
c,7/5+x-2/5=4
7/5+x=4+2/5
7/5+x=22/5
x=22/5-7/5
x=15/5
x=3
d,1 3/4+x-7/8=5
7/4+x-7/8=5
7/4+x=5+7/8
7/4+x=47/8
x=47/8-7/4
x=47/8-14/8
x=33/8
a)\(\frac{-3}{5}+\frac{1}{4}+\frac{-3}{10}\)
\(=\frac{-12}{20}+\frac{5}{20}+\frac{-6}{20}\)
\(=\frac{-13}{20}\)
b)\(\frac{1}{5}+\frac{-9}{10}+\frac{-7}{25}=\frac{10}{50}+\frac{-45}{50}+\frac{-14}{50}=\frac{-49}{50}\)
c)\(\frac{1}{5}+\frac{-1}{6}+\frac{1}{7}+\frac{-1}{8}+\frac{1}{9}+\frac{1}{8}+\frac{-1}{7}+\frac{1}{6}+\frac{-1}{5}\)
=\(\left(\frac{1}{5}+\frac{-1}{5}\right)+\left(\frac{-1}{6}+\frac{1}{6}\right)+\left(\frac{1}{7}+\frac{-1}{7}\right)+\left(\frac{1}{8}+\frac{-1}{8}\right)+\frac{1}{9}\)
=\(0+0+0+0+\frac{1}{9}\)
=\(\frac{1}{9}\)
a) \(=\frac{1}{6}x\frac{5}{2}+\frac{3}{7}\)
\(=\frac{5}{12}+\frac{3}{7}\)
\(=\frac{71}{84}\)
b) \(=\frac{8}{5}-\frac{1}{2}x\frac{1}{3}\)
\(=\frac{8}{5}-\frac{1}{6}\)
\(=\frac{43}{30}\)
a, \(\frac{1}{6}:\frac{2}{5}+\frac{3}{7}\)
\(=\frac{1}{6}\cdot\frac{5}{2}+\frac{3}{7}\)
\(=\frac{5}{12}+\frac{3}{7}\)
\(=\frac{71}{84}\)
b, \(\frac{8}{5}-\frac{1}{2}\cdot\frac{1}{3}\)
\(=\frac{8}{5}-\frac{1}{6}\)
\(=\frac{43}{30}\)
\(\frac{7}{8}>\frac{7}{9}>\frac{7}{10}>\frac{7}{11}>\frac{7}{15}\)
Tính :
\(a,\frac{1}{4}+\frac{3}{8}+\frac{5}{16}=\frac{4+6+5}{16}=\frac{15}{16}\)
\(b,\frac{3}{5}-\frac{1}{3}-\frac{1}{6}=\frac{18-10-5}{30}=\frac{3}{30}=\frac{1}{10}\)
\(c,\frac{4}{7}\times\frac{5}{8}\times\frac{7}{12}=\frac{5}{14}\times\frac{7}{12}=\frac{5}{24}\)
\(d,\frac{25}{28}:\frac{15}{14}\times\frac{6}{7}=\frac{25\times14\times6}{28\times15\times7}=\frac{5}{7}\)
\(A=5\dfrac{3}{5}+7\dfrac{1}{8}+2,875+4,4\)
\(A=\dfrac{28}{5}+\dfrac{57}{8}+2,875+4,4\)
\(A=5,6+7,125+2,875+4,4\)
\(A=\left(5,6+4,4\right)+\left(7,125+2,875\right)\)
\(A=10+10\)
\(A=20\)