Tính :
a) \(\displaystyle {3 \over 5} \times {4 \over 7}\) | \(\displaystyle {{12} \over {35}}:{3 \over 5}\) |
\(\displaystyle {{12} \over {35}}:{4 \over 7}\) | \(\displaystyle {4 \over 7} \times {3 \over 5}\) |
b) \(\displaystyle {{13} \over {11}} \times 2\) | \(\displaystyle {{26} \over {11}}:{{13} \over {11}}\) |
\(\displaystyle {{26} \over {11}}:2\) | \(\displaystyle 2 \times {{13} \over {11}}\) |
a) \(\displaystyle {3 \over 5} \times {4 \over 7} = {{12} \over {35}};\)
\(\displaystyle {{12} \over {35}}:{3 \over 5} = {{12} \over {35}} \times {5 \over 3} = {4 \over 7};\)
\(\displaystyle {{12} \over {35}}:{4 \over 7} = {{12} \over {35}} \times {7 \over 4} = {3 \over 5};\)
\(\displaystyle {4 \over 7} \times {3 \over 5} = {{12} \over {35}}.\)
b) \(\displaystyle {{13} \over {11}} \times 2 ={{13 \times 2} \over {11}}= {{26} \over {11}};\)
\(\displaystyle {{26} \over {11}}:{{13} \over {11}} = {{26} \over {11}} \times {{11} \over {13}} = 2;\)
\(\displaystyle {{26} \over {11}}:2 ={{26} \over {11}} :{2\over 1}= {{26} \over {11}} \times {1 \over 2} = {{13} \over {11}};\)
\(\displaystyle 2 \times {{13} \over {11}} ={{2 \times 13} \over {11}} = {{26} \over {11}}\)
-- Mod Toán lớp 4