1、333387又二分之一*79+790*66664又四分之一
=(333387+1/2+666640+5/2)*79
=1000030*79
=79002370
2、 81.5*15.8+81.5*51.8+67.6*18.5
=81.5*(15.8+51.8)+67.6*(100-81.5)
=81.5*67.6+6760-67.6*81.5
=6760
3、(9又七分之二+7又九分之儿)/(七分之五+九分之五)
=(65/7+65/9)/(5/7+5/9)
=13*(5/7+5/9)/(5/7+5/9)
=13
4、 1/(2x4)+1/(4x6)+ ...+1/(48x50)
=1/2*(1/2-1/4+1/4-1/6+...+1/48-1/50)
=1/2*(1/2-1/50)
=12/50