Tính
a) − 1,6: 1 + 2 3
b) 7 30 + − 12 37 + 5 25 + − 25 37 + 23 30
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a) \(\dfrac{7}{30}+\dfrac{\left(-12\right)}{37}+\dfrac{23}{30}+\dfrac{\left(-25\right)}{37}=\left(\dfrac{7}{30}+\dfrac{23}{30}\right)+\left(\dfrac{-12}{37}+\dfrac{-25}{37}\right)=1+\left(-1\right)=0\)
b) \(\dfrac{5}{7}\cdot\dfrac{5}{11}+\dfrac{5}{7}\cdot\dfrac{2}{11}-\dfrac{5}{7}\cdot\dfrac{14}{11}=\dfrac{5}{7}\cdot\left(\dfrac{5}{11}+\dfrac{2}{11}-\dfrac{14}{11}\right)=\dfrac{5}{7}\cdot\left(-\dfrac{7}{11}\right)=-\dfrac{5}{11}\)
c) \(\dfrac{\left(-5\right)}{7}\cdot\dfrac{3}{13}-\dfrac{5}{7}\cdot\dfrac{10}{13}+1\dfrac{5}{7}=\dfrac{5}{7}\cdot\dfrac{-3}{13}-\dfrac{5}{7}\cdot\dfrac{10}{13}+\dfrac{12}{7}=\dfrac{5}{7}\cdot\left(\dfrac{-3}{13}-\dfrac{10}{13}\right)+\dfrac{12}{7}=\dfrac{5}{7}\cdot\left(-1\right)+\dfrac{12}{7}=\left(-\dfrac{5}{7}\right)+\dfrac{12}{7}=\dfrac{7}{7}=1\)
Bài 1:
b) (-17)+(-23)=-40
c) (-29)+36=7
d) 45+(-57)=-12
e) 105+(-5)=100
f) (-48)+(-14)=-62
g) (-75)+(-13)=-88
h) (-37)+23=-14
i) (-54)+(-46)=-100
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+31+32+33+34+35+36+37
=(1+37)x37:2
=703
a) − 1,6: 1 + 2 3 = − 16 10 : 3 3 + 2 3 = − 16 10 : 5 3 = − 16 10 . 3 5 = − 16.3 10.5 = − 8.3 5.5 = − 24 25 .
b) 7 30 + − 12 37 + 5 25 + − 25 37 + 23 30 = 7 30 + 23 30 + − 12 37 + − 25 37 + 5 25 = 30 30 + − 37 37 + 1 5 = 1 + − 1 + 1 5 = 1 5 .