答：依题意可知（1/4+1/6-1/2）×12＝1/4×12+1/6×12-1/2×12＝3+2-6＝5-6＝-1。
(1/4+1/6-1/2)*12=1/4*12+1/6*12-1/2*12=3+2-6=-1
