Question

tinh nhanh  

a 1/4 + 2/5 + 6/8 + 9/15 + 8/1                                                         b . 15/31 * 16/43 + 15/31 * 27/43

Answer 1

a) \(\frac{1}{4}+\frac{2}{5}+\frac{6}{8}+\frac{9}{15}+\frac{8}{1}\)

\(=\left(\frac{1}{4}+\frac{6}{8}\right)+\left(\frac{2}{5}+\frac{9}{15}\right)+\frac{8}{1}\)

\(=\left(\frac{1}{4}+\frac{3}{4}\right)+\left(\frac{2}{5}+\frac{3}{5}\right)+\frac{8}{1}\)

\(=\frac{4}{4}+\frac{5}{5}+\frac{8}{1}\)

\(=1+1+8\)

\(=10\)

b) \(\frac{15}{31}\cdot\frac{16}{43}+\frac{15}{31}\cdot\frac{27}{43}\)

\(=\frac{15}{31}\cdot\left(\frac{16}{43}+\frac{27}{43}\right)\)

\(=\frac{15}{31}\cdot\frac{43}{43}\)

\(=\frac{15}{31}\cdot1=\frac{15}{31}\)

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