摘要：1． 如图所示.有一个可以自由转动的圆形转盘.被平均分成四个扇形.四个扇形内分别标有数字1.2.-3.-4．若将转盘转动两次.每一次停止转动后.指针指向的扇形内的数字分别记为a.b(若指针恰好指在分界线上.则该次不计.重新转动一次.直至指针落在扇形内)． 请你用列表法或树状图求a与 b的乘积等于2的概率． .解:a与b的乘积的所有可能出现的结果如下表所示: a b 1 2 -3 -4 1 1 2 -3 -4 2 2 4 -6 -8 -3 -3 -6 9 12 -4 -4 -8 12 16 ········································································································· 6分 总共有16种结果.每种结果出现的可能性相同.其中ab=2的结果有2种. ·················································································································· 7分 ∴a与 b的乘积等于2的概率是. ······················································ 8分

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