(1*3*5+2*6*10+3*9*15)/(2*4*6+4*8*12+6*12*18)
=(1*3*5+2*1*3*5+3*1*3*5)/(2*4*6+2*2*4*6+3*2*4*6)
=(1+2+3)*1*3*5/[(1+2+3)*2*4*6]
=1*3*5/2*4*6
=5/16