题干

把大小完全相同的6个乒乓球分成两组,每组3个,每组乒乓球上面分别标有数字1,2,3,将这两组乒乓球分别放入两个盒子中搅匀,再从每个盒子中各随机取出1个乒乓球,请用画树状图(或列表)的方法,求取出的2个乒乓球上面数字之和为偶数的概率.
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答案(点此获取答案解析)

解:画树状图为:

共有9种等可能的结果数,其中取出的2个乒乓球上面数字之和为偶数的结果数为5,

所以取出的2个乒乓球上面数字之和为偶数的概率=

同类题1

完形填空

    A poor farmer had a friend who was famous for the wonderful apples he grew. One day, his friend gave him a young apple tree and told him to take it home and 1 it.

    Seeing the gift, the farmer was very happy, and he thought he would also have a lot of wonderful apples, but when he got home, he felt 2 . He did not know where to plant it. He thought over and over and considered every place he could think of. 3 , he decided to plant the tree in his woods. There were many high trees with thick leaves in the woods. With those trees around ,no one else could see the young apple tree. He even felt proud of himself for finding so secret a place for the apple tree. Every day he went to take care of the tree, watering it. To his surprise and 4, the apple tree didn't grow as well as he expected.  It died without sunlight and good soil.

    Later the friend asked the farmer why he had planted the tree in such a 5place. "What's the difference?" the farmer said angrily. "If I had planted the tree near the6, passers-by(行人) would have stolen the fruit. If I had planted the tree in one of my fields, my neighbors would have come at night and 7 some of the apples! If I had planted it near my house, my own children would have taken the fruits. No matter where I plant the tree, I can't have8 to enjoy the apples: So there is no difference where I planted it."

    "Yes," said the friend. "But sooner or later someone could have enjoyed the fruit. Now you not only have robbed(抢夺) everyone of the fruit, but also have 9 a good apple tree! You don't know the true meaning of 'share'!"

    We should learn to 10in our life. The more you want to own something all by yourself, the less you get at last.