从一副未曾启封的扑克牌中取出1张红桃,2张黑桃的牌共3张,洗匀后,从这3张牌中任取1张牌恰好是黑桃的概率是 .
计算:21×3.14-31×3.14=_________.
-15a2+5a=________(3a-1);
因式分解:km+kn=_________;
3a2-6ab+a=_________(3a-6b+1);
多项式32p2q3-8pq4m的公因式是_________;