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\(\dfrac{5}{3}+\dfrac{5}{12}+\dfrac{5}{20}+\dfrac{5}{30}+...+\dfrac{5}{9900}=\dfrac{5}{3}+5\left(\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{99.100}\right)=\dfrac{5}{3}+5\left(\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{99}-\dfrac{1}{100}\right)=\dfrac{5}{3}+5\left(\dfrac{1}{3}-\dfrac{1}{100}\right)=3\dfrac{23}{60}\).
\(\frac{5}{6}+\frac{5}{12}+\frac{5}{20}+......+\frac{5}{110}\)
\(=\frac{5}{2.3}+\frac{5}{3.4}+\frac{5}{4.5}+..........+\frac{5}{10.11}\)
\(=5\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+..........+\frac{1}{10.11}\right)\)
\(=5\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...........+\frac{1}{10}-\frac{1}{11}\right)\)
\(=5\left(\frac{1}{2}-\frac{1}{11}\right)\)
\(=5.\frac{9}{22}=\frac{45}{22}\)
30 + 12 + ( - 20 ) + ( - 12 )
= 30 + 12 - 20 - 12
= 42 - 20 - 12
= 22 - 12
= 10
a,(-17)+5+8+17=[(-17)+17]+5+8=0+13=13
b. 30+12+(-20)+(-12)=[12+(-12)]+30+(-20)=0+10=10
Nho k minh nha
\(20-\left[30-\left(5-1^2\right)\right]\)
\(=20-\left[30-\left(5-1\right)\right]\)
\(=20-\left(30-4\right)\)
\(=20-26\)
\(=-6\)
\(20-\left[30-\left(5-1^2\right)\right]\\ =20-\left[30-\left(5-1\right)\right]\\ =20-\left[30-4\right]\\ =20-26\\ =-6.\)