文 [1 ]解决了一类典型且较复杂的数学期望问题 (见例 1 ) .笔者颇受启示 ,经探讨得如下简解 .引理 1　袋中有红球 m个 ,白球 n个 ,现不放回地从袋中摸球 ,则第 k次取到红球的概率为 mm + n( k =1 ,2 ,… ,m + n) .证明　令 Ak =第 k次摸到红球 ,用数学归纳法证明 P( Ak) =mm + The paper [1] solves a typical and more complex mathematical expectation problem (see example 1). The author is quite enlightened and has been discussed as follows. The Lemma 1 bag contains m red balls and n white balls. If you touch the ball from the bag without putting it back, the probability of getting the red ball at the kth time is mm + n( k =1 ,2 ,... ,m + n). Prove that Ak =k touch the red ball for the kth time. Proving P( Ak) = mm + with Mathematical Induction