Giải bài 2 trang 167 - SGK Toán lớp 4
Tính:
a) \(\dfrac{2}{7}+ \dfrac{3}{5};\) \(\dfrac{31}{35}-\dfrac{2}{7};\)
\(\dfrac{31}{35}-\dfrac{3}{5};\) \(\dfrac{3}{5}+ \dfrac{2}{7};\)
b) \(\dfrac{3}{4}+ \dfrac{1}{6};\) \(\dfrac{11}{12}-\dfrac{3}{4};\)
\(\dfrac{11}{12}-\dfrac{3}{6};\) \(\dfrac{1}{6}+ \dfrac{3}{4}.\)
a) \(\dfrac{2}{7}+ \dfrac{3}{5}=\dfrac{10}{35}+ \dfrac{21}{35}=\dfrac{31}{35}\)
\(\dfrac{31}{35}-\dfrac{2}{7}=\dfrac{31}{35}-\dfrac{10}{35}=\dfrac{21}{35}=\dfrac{3}{5}\)
\(\dfrac{31}{35}-\dfrac{3}{5}=\dfrac{31}{35}-\dfrac{21}{35}=\dfrac{10}{35}=\dfrac{2}{7}\)
\(\dfrac{3}{5}+ \dfrac{2}{7}=\dfrac{21}{35}+ \dfrac{10}{35}=\dfrac{31}{35}\)
b)
\(\dfrac{3}{4}+ \dfrac{1}{6}=\dfrac{9}{12}+ \dfrac{2}{12}=\dfrac{11}{12}\)
\(\dfrac{11}{12}-\dfrac{3}{4} =\dfrac{11}{12}-\dfrac{9}{12}=\dfrac{2}{12}=\dfrac{1}{6}\)
\(\dfrac{11}{12}-\dfrac{3}{6}=\dfrac{11}{12}-\dfrac{6}{12}=\dfrac{5}{12}\)
\(\dfrac{1}{6}+ \dfrac{3}{4}=\dfrac{2}{12}+ \dfrac{9}{12}=\dfrac{11}{12}\)