Question

trả lời cho mik mấy câu này nhé cảm ơn làm đúng mik tick cho

a) \(4,5:\left[\left(1\dfrac{1}{2}-\dfrac{5}{3}\right)-\dfrac{9}{5}+2,4\right]-\dfrac{1}{7}\)

b) \(4\dfrac{1}{3}:\left(25\%+1,25\right)-6\dfrac{2}{3}\)

c)\(\dfrac{5}{1.4}+\dfrac{5}{4.7}+\dfrac{5}{7.10}+.......+\dfrac{5}{91.94}\)

Answer 1

a) \(4,5:\left[\left(\dfrac{9-10}{6}\right)-\dfrac{9}{5}+\dfrac{12}{5}\right]-\dfrac{1}{7}\)

\(=4,5:\left(\dfrac{-1}{6}-\dfrac{-3}{5}\right)-\dfrac{1}{7}\)

=\(4,5:\left(\dfrac{-5+18}{30}\right)-\dfrac{1}{7}\)

=\(4,5:\dfrac{13}{30}-\dfrac{1}{7}\)=\(\dfrac{135}{13}-\dfrac{1}{7}=\dfrac{932}{91}\)

b) \(\dfrac{13}{3}:\left(\dfrac{1}{4}+\dfrac{5}{4}\right)-\dfrac{20}{3}\)

=\(\dfrac{13}{3}.\dfrac{2}{3}-\dfrac{20}{3}\)=\(\dfrac{26}{9}-\dfrac{20}{3}=\dfrac{26}{9}-\dfrac{60}{9}=\dfrac{-34}{9}\)

c) \(5.\left(\dfrac{1}{1.4}+\dfrac{1}{4.7}+.....+\dfrac{1}{91.94}\right)\)

\(=5.\left[\dfrac{1}{3}\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{91}-\dfrac{1}{94}\right)\right]\)

\(=5.\left[\dfrac{1}{3}.\left(1-\dfrac{1}{94}\right)\right]\)

=\(5.\left(\dfrac{1}{3}.\dfrac{93}{94}\right)\)

\(=5.\dfrac{31}{94}=\dfrac{155}{94}\)

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