2 câu trả lời
\[\begin{array}{l} 15.37.4 + 120.21 + 21.5.12\\ = 15.4.37 + 21\left( {120 + 5.12} \right)\\ = 60.37 + 21.\left( {120 + 60} \right)\\ = 2220 + 21.180\\ = 2220 + 3780\\ = 6000. \end{array}\]
\[\begin{array}{l} 15.37.4 + 120.21 + 21.5.12\\ = 15.4.37 + 21\left( {120 + 5.12} \right)\\ = 60.37 + 21.\left( {120 + 60} \right)\\ = 2220 + 21.180\\ = 2220 + 3780\\ = 6000. \end{array}\]