Giải bài 1 trang 153 - SGK Toán lớp 4

Tính:

a) $\dfrac{3}{5} + \dfrac{11}{20}= \dfrac{12}{20} + \dfrac{11}{20}=\dfrac{12+ 11}{20} = \dfrac{23}{20}$         

b) $\dfrac{5}{8}-\dfrac{4}{9}=\dfrac{45}{72} -\dfrac{32}{72}=\dfrac{45-32}{72} = \dfrac{13}{72}$     

c) $\dfrac{9}{16}\,\times\,\dfrac{4}{3}= \dfrac{9\,\times\,4}{16\,\times\,3} =\dfrac{36}{48}=\dfrac{3}{4}$

d) $\dfrac{4}{7}:\dfrac{8}{11} =\dfrac{4}{7}\times\dfrac{11}{8}=\dfrac{44}{56}=\dfrac{11}{14}$       

e) $\dfrac{3}{5}+\dfrac{4}{5}:\dfrac{2}{5}=\dfrac{3}{5}+\dfrac{4}{5}\times\dfrac{5}{2}=\dfrac{3}{5}+\dfrac{20}{10}=\dfrac{3}{5}+\dfrac{10}{5}=\dfrac{13}{5}$