Tính:
a) \(\displaystyle {4 \over 9}:{5 \over 7}\) b) \(\displaystyle {1 \over 3}:{1 \over 4}\)
\(\displaystyle {5 \over 7}:{4 \over 9}\) \(\displaystyle {1 \over 4}:{1 \over 3}\)
a) \(\displaystyle {4 \over 9}:{5 \over 7} = {4 \over 9} \times {7 \over 5} = {{28} \over {45}}\)
\(\displaystyle {5 \over 7}:{4 \over 9} = {5 \over 7} \times {9 \over 4} = {{45} \over {28}}\)
b) \(\displaystyle {1 \over 3}:{1 \over 4} = {1 \over 3} \times {4 \over 1} = {4 \over 3}\)
\(\displaystyle {1 \over 4}:{1 \over 3} = {1 \over 4} \times {3 \over 1} = {3 \over 4}\)
-- Mod Toán lớp 4