Tính \(\displaystyle {7 \over 5} + {4 \over 3} + {7 \over 5} + {4 \over 3}\) bằng 2 cách.
Cách 1:
\(\displaystyle {7 \over 5} + {4 \over 3} + {7 \over 5} + {4 \over 3} = {7 \over 5} \times 2 + {4 \over 3} \times 2= ... \)
Cách 2:
\(\displaystyle {7 \over 5} + {4 \over 3} + {7 \over 5} + {4 \over 3} = \left( {{7 \over 5} + {4 \over 3}} \right) \times 2= ...\)
Cách 1:
\(\displaystyle {7 \over 5} + {4 \over 3} + {7 \over 5} + {4 \over 3} \\ \displaystyle = {7 \over 5} \times 2 + {4 \over 3} \times 2 \\\displaystyle = {{14} \over 5} + {8 \over 3} \\\displaystyle={42 \over 15}+ {{ 40} \over {15}} = {{82} \over {15}}\)
Cách 2:
\(\displaystyle {7 \over 5} + {4 \over 3} + {7 \over 5} + {4 \over 3} \\= \displaystyle\left( {{7 \over 5} + {4 \over 3}} \right) \times 2 \\ \displaystyle = \left( {21\over 15} +{{{ 20} \over {15}}} \right) \times 2 \\ \displaystyle= {{41} \over {15}} \times 2 = {{82} \over {15}}\)
-- Mod Toán lớp 4