问一道数学题,涉及到微分方程atankcontains4lbsofsaltdissolvedin100gallonsofwater.Supposethatbrinecontaining2lbsofsaltpergallonofwaterisallowedtoenterthetankatarateof5gallons/minute,andthatthemixedsolu

　　问一道数学题,涉及到微分方程

　　atankcontains4lbsofsaltdissolvedin100gallonsofwater.Supposethatbrinecontaining2lbsofsaltpergallonofwaterisallowedtoenterthetankatarateof5gallons/minute,andthatthemixedsolutionisdrainedfromthetankatthesamerate.Usethedifferentialequationtofindtheamountofsaltafter10minutes.

　　大致翻译下:

　　一个水缸有盐水,此盐水由4磅的盐溶解在100加仑水里.

　　假设把[2磅盐/1加仑的盐水]往这个水缸里灌入,速度是5加仑/分钟,同样的,灌入的同时,此水缸以相同的速度往外漏水.

　　请问10分钟后这个水缸里还有多少盐?