Bài 2 trang 10 SGK Toán 5

Tính:

a)  \(3 + \dfrac{2}{5}\) ;             b) \( 4 -\dfrac{5}{7}\) ;              c) \( 1 - \left ( \dfrac{2}{5} +\dfrac{1}{3}\right )\).

Lời giải

a)  \( 3 +\dfrac{2}{5}=  \dfrac{3}{1}+\dfrac{2}{5}=  \dfrac{15}{5}+\dfrac{2}{5}=\dfrac{17}{5}\);

b)  \( 4 -\dfrac{5}{7}= \dfrac{4}{1}-\dfrac{5}{7} =  \dfrac{28}{7}-\dfrac{5}{7}=\dfrac{23}{7}\);

c)   \( 1 -\left ( \dfrac{2}{5} +\dfrac{1}{3}\right )  = 1 -\left ( \dfrac{6}{15} +\dfrac{5}{15}\right )\)  \( = 1 -\dfrac{11}{15} =  \dfrac{15}{15}-\dfrac{11}{15}=\dfrac{4}{15}\).


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