1+1=21+2=31+3=41+4=52+2=42+3=52+4=62+1=33+1=43+2=53+3=63+4=74+1=54+2=64+3=74+4=8一共16种小于5的概率是3/8
3/C42
2/6约等于0.33
1,2 1,3/c42=2/6=1/3