Tính theo mẫu:
Mẫu: \(\displaystyle{{5 \times 6 \times 7\times 9} \over {12 \times 7 \times 27}} = {{5 \times \not{6} \times \not{7}\times \not{9}} \over {\not{6} \times 2 \times \not{7} \times \not{9} \times 3}} \displaystyle = {5 \over {6}}.\)
a) \(\displaystyle {{3 \times 4 \times 7} \over {12 \times 8 \times 9}}\)
b) \(\displaystyle {{4 \times 5 \times 6} \over {12 \times 10 \times 8}}\)
c) \(\displaystyle {{5 \times 6 \times 7} \over {12 \times 14 \times 15}}\)
a) \(\displaystyle {{3 \times 4 \times 7} \over {12 \times 8 \times 9}} \displaystyle= \dfrac{\not{3}\times \not{4}\times 7} {\not{3}\times \not{4} \times 8 \times 9}=\dfrac{7}{72}\)
b) \(\displaystyle {{4 \times 5 \times 6} \over {12 \times 10 \times 8}} \displaystyle= \dfrac{\not{4}\times \not{5}\times \not{6}} {\not{6}\times 2 \times \not{5}\times 2 \times \not{4} \times 2}=\dfrac{1}{8}\)
c) \(\displaystyle {{5 \times 6 \times 7} \over {12 \times 14 \times 15}}\displaystyle= \dfrac{\not{5}\times \not{6}\times \not{7}} {\not{6}\times 2 \times \not{7}\times 2 \times \not{5} \times 3}=\dfrac{1}{12}\)
-- Mod Toán lớp 4