Bài 38 trang 40 Vở bài tập toán 6 tập 2

Đề bài

Tính:

a) \(\dfrac{1}{8}-\dfrac{1}{2}\) ;               b) \(\dfrac{-11}{12}-(-1)\) ;

c) \(\dfrac{3}{5}-\dfrac{5}{6}\) ;               d) \(\dfrac{-1}{16}-\dfrac{1}{15}\)

e) \(\dfrac{11}{36}-\dfrac{-7}{24}\) ;         g) \(\dfrac{-5}{9}-\dfrac{-5}{12}.\) 

Lời giải chi tiết

a) \(\dfrac{1}{8}-\dfrac{1}{2}=\dfrac{1}{8}+ \dfrac{-1}{2}\)\(=\dfrac{1}{8}+\dfrac{-4}{8}=\dfrac{-3}{8}\).

b) \(\dfrac{-11}{12}-(-1)=\dfrac{-11}{12}+1\)\(=\dfrac{-11}{12}+\dfrac{12}{12}=\dfrac{1}{12}.\)

c) \(\dfrac{3}{5}-\dfrac{5}{6}=\dfrac{3}{5}+\left (-\dfrac{5}{6} \right )\)\(=\dfrac{{18}}{{30}} + \left( {\dfrac{{ - 25}}{{30}}} \right)=\dfrac{-7}{30}.\)

d)  \(\dfrac{{ - 1}}{{16}} - \dfrac{1}{{15}} = \dfrac{{ - 1}}{{16}} + \left( { - \dfrac{1}{{15}}} \right) \)\(= \dfrac{{ - 15}}{{240}} + \left( { - \dfrac{{16}}{{240}}} \right)\)\( = \dfrac{{ - 31}}{{240}}\)

e) \(\dfrac{{11}}{{36}} - \dfrac{{ - 7}}{{24}} \)\(= \dfrac{{11}}{{36}} + \dfrac{7}{{24}} \)\(= \dfrac{{22}}{{72}} + \dfrac{{21}}{{72}}\)\( = \dfrac{{43}}{{72}}\)                    

g) \(\dfrac{{ - 5}}{9} - \dfrac{{ - 5}}{{12}} = \dfrac{{ - 5}}{9} + \dfrac{5}{{12}} \)\(= \dfrac{{ - 20}}{{36}} + \dfrac{{15}}{{36}} = \dfrac{-5}{{36}}\) 

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