2/2*4+8/4*6+2/6*8+2/8*10+2/10*12
=(1/2-1/4)+(1/4-1/6)+(1/6-1/8)+(1/8-1/10)+(1/10-1/12)
=1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12
=1/2-1/12=5/12