Giải bài 1 trang 169 - SGK Toán lớp 4
Tính bằng hai cách:
a) (611+511)×37;
b) 35×79−35×29
c) (67−47):25;
d) 815:211+715:211
a)(611+511)×37;
Cách 1:
(611+511)×37=1×37=37
Cách 2:
(611+511)×37=611×37+511×37=1877+1577=3377=37
b) 35×79−35×29
Cách 1:
\dfrac{3}{5} \times \dfrac{7}{9} - \dfrac{3}{5} \times \dfrac{2}{9}\\=\dfrac{21}{45}-\dfrac{6}{45}=\dfrac{15}{45}= \dfrac{1}{3}
Cách 2:
\dfrac{3}{5} \times \dfrac{7}{9} - \dfrac{3}{5} \times \dfrac{2}{9}\\=\dfrac{3}{5} \times (\dfrac{7}{9}-\dfrac{2}{9})\\=\dfrac{3}{5} \times \dfrac{5}{9}= \dfrac{15}{45}= \dfrac{1}{3}
c) (\dfrac{6}{7}-\dfrac{4}{7}) : \dfrac{2}{5};
Cách 1:
(\dfrac{6}{7}-\dfrac{4}{7}) : \dfrac{2}{5}\\=\dfrac{2}{7} : \dfrac{2}{5}\\=\dfrac{2}{7} \times\dfrac{5}{2}=\dfrac{10}{14}=\dfrac{5}{7}
Cách 2:
(\dfrac{6}{7}-\dfrac{4}{7}) : \dfrac{2}{5}\\=\dfrac{6}{7} : \dfrac{2}{5}-\dfrac{4}{7} : \dfrac{2}{5}\\=\dfrac{6}{7} \times\dfrac{5}{2}-\dfrac{4}{7} \times\dfrac{5}{2}\\=\dfrac{30}{14}-\dfrac{20}{14}=\dfrac{10}{14}=\dfrac{5}{7}
d) \dfrac{8}{15} : \dfrac{2}{11} + \dfrac{7}{15} : \dfrac{2}{11}
Cách 1:
\dfrac{8}{15} : \dfrac{2}{11} + \dfrac{7}{15} : \dfrac{2}{11} \\=\dfrac{8}{15} \times\frac{11}{2} + \dfrac{7}{15} \times\dfrac{11}{2} \\=\dfrac{88}{30} +\dfrac{77}{30} =\dfrac{165}{30} =\dfrac{11}{2}
Cách 2:
\dfrac{8}{15} : \dfrac{2}{11} + \dfrac{7}{15} : \dfrac{2}{11} \\=(\dfrac{8}{15} + \frac{7}{15}) : \dfrac{2}{11}\\=1 \times\dfrac{11}{2} \\=\dfrac{11}{2}
