7/29*3/8+6/29*7/12+3/29*7/9
=7/29x3/8+7/29x1/2+7/29x1/3
=7/29x(3/8+1/2+1/3)
=7/29x(9/24+12/24+8/24)
=7/29x29/24
=7/24
如果本题有什么不明白可以追问,请看清楚题目你抄错了，中间是加号的，