Bài 1 trang 164 SGK Toán 5

Tính:

a) \(\dfrac{12}{17}:6\)  ;                     \(16:\dfrac{8}{11}\)  ;                       \(9: \dfrac{3}{5}\times\dfrac{4}{15}\) ;

b) \(72  :45\)                         \(281,6 : 8\)                        \(300,72 : 53,7\)

    \(15 : 50\)                         \(912,8 : 28\)                       \(0,162 : 0,36\)

Lời giải

a) \(\dfrac{12}{17} : 6 = \dfrac{12}{17} \times \dfrac{1}{6} = \dfrac{12}{17 \times 6} \)\(= \dfrac{6 \times 2}{17 \times 6} =\dfrac{2}{17}\)

\(16 :  \dfrac{8}{11} = 16 \times  \dfrac{11}{8} = \dfrac{16\times 11}{8} \)

\(= \dfrac{8 \times 2\times 11}{8} = 22\) 

\(\eqalign{ & 9:{3 \over 5} \times {4 \over {15}} = 9 \times {5 \over 3} \times {4 \over {15}}  \cr  &  = {{9 \times 5 \times 4} \over {3 \times 15}} = {{3 \times 3 \times 5 \times 4} \over {3 \times 3 \times 5}} = 4 \cr} \)


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