Quoc Tran Anh Le Coordinator
31/07/2018 at 02:21-
Tôn Thất Khắc Trịnh 31/07/2018 at 08:06\(v_{tb}=\dfrac{s+s}{t_1+t_2}=\dfrac{2s}{\dfrac{s}{v_1}+\dfrac{s}{v_2}}=\dfrac{2}{\dfrac{v_1+v_2}{v_1v_2}}=\dfrac{2v_1v_2}{v_1+v_2}=\dfrac{2\cdot4\cdot12}{4+12}=\dfrac{96}{16}=6\left(mph\right)\)
Quoc Tran Anh Le selected this answer.