Viết phân số thích hợp vào chỗ chấm:
a) \(\displaystyle{4 \over 5} + {2 \over 3} = {2 \over 3} + ...\) \(\displaystyle{{13} \over {25}} + {3 \over 7} = {3 \over 7} + ...\)
b) \(\displaystyle\left( {{2 \over 3} + {3 \over 4}} \right) + {1 \over 2} = {2 \over 3} + \left( {{3 \over 4} + ...} \right)\)
\(\displaystyle{2 \over 3} + \left( {{3 \over 4} + {1 \over 2}} \right) = \left( {... + {3 \over 4}} \right) + {1 \over 2}\)
a) \(\displaystyle{4 \over 5} + {2 \over 3} = {2 \over 3} + {4 \over 5}\) \(\displaystyle{{13} \over {25}} + {3 \over 7} = {3 \over 7} + {{13} \over {25}}\)
b) \(\displaystyle\left( {{2 \over 3} + {3 \over 4}} \right) + {1 \over 2} = {2 \over 3} + \left( {{3 \over 4} + {1 \over 2}} \right)\)
\(\displaystyle{2 \over 3} + \left( {{3 \over 4} + {1 \over 2}} \right) = \left( {{2 \over 3} + {3 \over 4}} \right) + {1 \over 2}\)
-- Mod Toán lớp 4