Bài 1:
a: \(\dfrac{-7}{27}+\dfrac{-8}{27}=\dfrac{-7-8}{27}=-\dfrac{15}{27}=-\dfrac{5}{9}\)
b: \(\dfrac{1}{2}+\dfrac{13}{19}-\dfrac{4}{9}+\dfrac{6}{19}+\dfrac{5}{18}\)
\(=\left(\dfrac{1}{2}-\dfrac{4}{9}+\dfrac{5}{18}\right)+\left(\dfrac{13}{19}+\dfrac{6}{19}\right)\)
\(=\dfrac{9-8+5}{18}+1=\dfrac{1}{3}+1=\dfrac{4}{3}\)
c: \(\left(\dfrac{23}{41}-\dfrac{15}{82}\right):\dfrac{15}{41}\)
\(=\left(\dfrac{46}{82}-\dfrac{15}{82}\right):\dfrac{15}{41}\)
\(=\dfrac{31}{82}\cdot\dfrac{41}{15}=\dfrac{31}{30}\)
d: \(\dfrac{4}{3}+\dfrac{-11}{31}+\dfrac{3}{10}-\dfrac{20}{31}-\dfrac{2}{5}\)
\(=\left(\dfrac{4}{3}+\dfrac{3}{10}-\dfrac{2}{5}\right)+\dfrac{-11-20}{31}\)
\(=\dfrac{40+9-12}{30}-1=\dfrac{49-12-30}{30}=\dfrac{7}{30}\)
e: \(\dfrac{5}{7}\cdot\dfrac{5}{11}+\dfrac{5}{7}\cdot\dfrac{2}{11}-\dfrac{5}{7}\cdot\dfrac{14}{11}\)
\(=\dfrac{5}{7}\left(\dfrac{5}{11}+\dfrac{2}{11}-\dfrac{14}{11}\right)\)
\(=\dfrac{5}{7}\cdot\dfrac{-7}{11}=-\dfrac{5}{11}\)
f: \(\dfrac{2}{11}\cdot\dfrac{-5}{4}+\dfrac{-9}{11}\cdot\dfrac{5}{4}+1\dfrac{3}{4}\)
=\(\dfrac{-5}{4}\left(\dfrac{2}{11}+\dfrac{9}{11}\right)+\dfrac{7}{4}\)
\(=\dfrac{-5}{4}+\dfrac{7}{4}=\dfrac{2}{4}=\dfrac{1}{2}\)
Bài 2:
a: \(60,7+25,5-38,7\)
\(=\left(60,7-38,7\right)+25,5\)
=22+25,5
=47.5
b: \(\left(-9,207\right)+3.8+\left(-1,5030\right)-2,8\)
\(=\left(-9,207-1,503\right)+\left(3,8-2,8\right)\)
=-10,71+1
=-9,71
c: \(\left(-12,5\right)+17,55+\left(-3,5\right)-\left(-2,45\right)\)
\(=\left(-12,5-3,5\right)+\left(17,55+2,45\right)\)
=20-16
=4
d: \(721,9\cdot75+25\cdot721,9\)
\(=721,9\cdot\left(75+25\right)\)
\(=721,9\cdot100=72190\)
e: \(\left(2,07+3,005\right)-\left(12,005-4,23\right)\)
\(=2,07+3,005-12,005+4,23\)
=6,3-9
=-2,7
f: \(4,35-\left(2,67-1,65\right)+\left(3,54-6,33\right)\)
\(=4,35-2,67+1,65+3,54-6,33\)
\(=\left(4,35+1,65\right)+\left(-2,67-6,33\right)+3,54\)
=6-9+3,54
=3,54-3
=0,54
g: \(\left(-0.4\right)\cdot\left(-0,5\right)\cdot\left(-0,8\right)\)
\(=-0,4\cdot0,5\cdot0,8\)
\(=-0,4\cdot0,4=-0,16\)
h: \(\left(-1,6\right)\cdot\left(-0,125\right)\cdot\left(-0,5\right)\)
\(=-1,6\cdot0,125\cdot0,5\)
\(=-0,8\cdot0,125=-0,1\)
