(,left( {frac{7}{4} - frac{3}{5}} right) times 20)
Giải chi tiết:
(begin{array}{l},left( {frac{7}{4} - frac{3}{5}} right) times 20 = left( {frac{{35}}{{20}} - frac{{12}}{{20}}} right) times 20\,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, = ,,,,,frac{{23}}{{20}} times 20\,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, = ,,,,,,23end{array})
Chọn B