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MT
3 tháng 8 2018
Ta có: \(A=1-2+3-4+5-6+7-8+9\)
\(=(1+9)-(2+8)+(3+7)-(4+6)+5\)
\(=10-10+10-10+5\)
\(=5\)
Vậy \(A=5\)
14 tháng 2 2020
B = 12 - 14 + 16 - 18 + ... + 2008 - 2010
B = -2 + (-2)+ (-2)+ (-2) + ...+ (-2)
B = -2 . 100
B = -200
U
10 tháng 8 2018
\(a,\frac{7}{15}\cdot\frac{4}{5}+\frac{7}{15}\cdot\frac{1}{5}-\frac{7}{15}\)
\(=\frac{7}{15}\left(\frac{4}{5}+\frac{1}{5}-1\right)\)
\(=\frac{7}{15}\cdot0\)
\(=0\)
\(b,\frac{9}{25}\cdot\frac{7}{18}+\frac{9}{26}\cdot\frac{1}{3}+\frac{9}{25}\cdot\frac{1}{9}\)
\(=\frac{9}{25}\left(\frac{7}{18}+\frac{1}{3}+\frac{1}{9}\right)\)
\(=\frac{9}{25}\cdot\frac{5}{6}\)
\(=\frac{3}{10}\)
8 tháng 4 2023
1)\(\dfrac{2}{9}+\dfrac{-3}{4}+\dfrac{5}{30}\)
\(=\dfrac{2.20}{9.20}+\dfrac{-3.45}{4.45}+\dfrac{5.6}{30.6}\)
\(=\dfrac{40}{180}+\dfrac{-135}{180}+\dfrac{30}{180}\)
\(=\dfrac{40+\left(-135\right)+30}{180}\)
\(=\dfrac{-65}{180}\)
\(=\dfrac{-13}{36}\)
2)\(\dfrac{-7}{12}-\dfrac{11}{18}\)
\(=\dfrac{-7.3}{12.3}-\dfrac{11.2}{18.2}\)
\(=\dfrac{-21}{36}-\dfrac{22}{36}\)
\(=\dfrac{-21-22}{36}\)
\(=\dfrac{-43}{36}\)
3)\(\dfrac{7}{8}-\dfrac{-5}{16}\)
\(=\dfrac{7.2}{8.2}-\dfrac{-5}{16}\)
\(=\dfrac{14}{16}-\dfrac{-5}{16}\)
\(=\dfrac{14-\left(-5\right)}{16}\)
\(=\dfrac{19}{16}\)
4)\(\dfrac{3}{8}-\dfrac{-9}{10}-\dfrac{5}{16}\)
\(=\dfrac{3.10}{8.10}-\dfrac{-9.8}{10.8}-\dfrac{5.5}{16.5}\)
\(=\dfrac{30}{80}-\dfrac{-72}{80}-\dfrac{25}{80}\)
\(=\dfrac{30-\left(-72\right)-25}{80}\)
\(=\dfrac{77}{80}\)
22 tháng 12 2021
1+2+3+4+5+6+7+8+9+10=55
11+12+13+14+15+16+17+18+19+20=155
1+2+3+4+5+6+7+8+9+10+11+12+13+14 +15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30-50-53=362
22 tháng 12 2021
1+2+3+4+5+6+7+8+9+10=55
11+12+13+14+15+16+17+18+19+20=155
1+2+3+4+5+6+7+8+9+10+11+12+13+14 +15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30-50-53=362
28 tháng 2 2019
a) (-48):2+26x(-2)
= (-24) + (-52)
= -76
b) (-96):(-2)+11x(-)?????
SAI ĐỀ
c) (-58)x(-2)+(-5)x(-8)
=116+40
=156
d) 3x(-7)-4x(-3)
=( -21) - (-12)
= (-21)+12
= -9
e) (-8)x(-4)+21x2
=32+42
=74
g) (-16)+32+(-18)x(-2)
= (-16) + 32 + 36
= 16 + 18
= 34
i) (-48)+(-2)x7+(-56):2+4x(-2)
= (-48)+(-14)+(-28)+(-8)
=(-62)+(-28)+(-8)
=(-90)+(-8)
=-98
h) (-16)-18+(-11)x(-2)+(-21)
=(-16)-18+22+(-21)
=(-34)+22-21
=(-34)+1
=-33
k) -18-(-3)x2+32-(-58)
=(-18)+3 x 2 + 32 + 58
=(-18) +6 +32 +58
=(-12)+32+58
= 20+58
=78
m) -2x8-72+31x(-2)
=(-16)-72+(-62)
=(-88)+(-62)
=-150
\(\left(\frac{7}{16}+\frac{-1}{18}+\frac{9}{32}\right):\frac{5}{4}\)
\(\left(\frac{7}{16}+\frac{-1}{18}+\frac{9}{32}\right).\frac{4}{5}\)
\(=\frac{7}{16}.\frac{4}{5}+\frac{-1}{18}.\frac{4}{5}+\frac{9}{32}.\frac{4}{5}\)
\(=\frac{7}{20}-\frac{2}{45}+\frac{9}{40}\)
\(=\frac{191}{360}\)
\(\left(\frac{7}{16}+\frac{-1}{18}+\frac{9}{32}\right):\frac{5}{4}\)
\(=\left(\frac{126}{288}+\frac{-16}{288}+\frac{81}{288}\right):\frac{5}{4}\)
\(=\frac{191}{288}:\frac{5}{4}\)
\(=\frac{191}{288}.\frac{4}{5}\)
\(=\frac{764}{1440}\)
\(=\frac{161}{360}\)
~HT~