Question

3)Tính nhanh (nếu có):

e)1/100 - 1/100.99 - 1/99.98 - ... - 1/3.2 - 1/2.1

g) -15,5 . 20,8 + 3,5.9,2 - 15,5.9,2 + 3,5.20,8

Answer 1

e) \(\frac{1}{100}-\frac{1}{100.99}-\frac{1}{99.98}-...-\frac{1}{3.2}-\frac{1}{2.1}\)

\(=\frac{1}{100}-\left(\frac{1}{100.99}+\frac{1}{99.98}+...+\frac{1}{3.2}+\frac{1}{2.1}\right)\)

\(=\frac{1}{100}-\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\right)\)

\(=\frac{1}{100}-\left(1-\frac{1}{100}\right)\)

\(=\frac{1}{100}-\frac{99}{100}\)

\(=\frac{-98}{100}\)\

\(=\frac{-49}{50}\)

g)-15,5 . 20,8 + 3,5.9,2 - 15,5.9,2 + 3,5.20,8

=20,8.(-15.5+3,5)+9,2(-15.5+3.5)

=(-15.5+3.5)(20.8+9.2)

=(-12).30

=-360

Answer 2

a) -49/50

b ) -360

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