有趣的加法(解pku1014的关键)

<shapetype id="_x0000_t75" stroked="f" filled="f" path="m@4@5l@4@11@9@11@9@5xe" o:preferrelative="t" o:spt="75" coordsize="21600,21600"><stroke joinstyle="miter"></stroke><formulas><f eqn="if lineDrawn pixelLineWidth 0"></f><f eqn="sum @0 1 0"></f><f eqn="sum 0 0 @1"></f><f eqn="prod @2 1 2"></f><f eqn="prod @3 21600 pixelWidth"></f><f eqn="prod @3 21600 pixelHeight"></f><f eqn="sum @0 0 1"></f><f eqn="prod @6 1 2"></f><f eqn="prod @7 21600 pixelWidth"></f><f eqn="sum @8 21600 0"></f><f eqn="prod @7 21600 pixelHeight"></f><f eqn="sum @10 21600 0"></f></formulas><path o:connecttype="rect" gradientshapeok="t" o:extrusionok="f"></path><lock aspectratio="t" v:ext="edit"></lock></shapetype><shape id="_x0000_i1025" style="WIDTH: 45.75pt; HEIGHT: 18pt" o:ole="" type="#_x0000_t75"><imagedata o:title="" src="file:///C:%5CDOCUME~1%5Cnew%5CLOCALS~1%5CTemp%5Cmsohtml1%5C01%5Cclip_image001.wmz"></imagedata></shape>用若干个1,2,3,4,5(可重用)这5个数字加出36的过程中，必有一个中间和数是6的倍数，为何？
例如5*5+4+4+3=36,期间已经有5*4+4=24了