Tính (theo mẫu):
Mẫu: \(\displaystyle {5 \over 7} \times {9 \over 5} = {{\not{5} \times 9} \over {7 \times \not{5}}} = {9 \over 7}\)
a) \(\displaystyle {3 \over 8} \times {8 \over 7}\) b) \(\displaystyle {{13} \over 7} \times {7 \over {13}}\)
a) \(\displaystyle {3 \over 8} \times {8 \over 7} = {{3 \times \not{8}} \over {\not{8} \times 7}} = {3 \over 7}\)
b) \(\displaystyle {{13} \over 7} \times {7 \over {13}} = {{\not{13} \times \not{7}} \over {\not{7} \times \not{13}}} = 1\)
-- Mod Toán lớp 4