请教三个数学问题

flyingjune

1.Six cards numbered from 1 to 6 are placed in an empty bowl.  First one card is drawn and then put back into the bowl; then a second card is drawn.  If the cards are drawn at random and if the sum of the numbers on the cards is 8, what is the probability that one of the two cards drawn is numbered 5 ?

  答案是2/5，而我做出来却变成了1/3 －－！！

2.cube是不是就一定是指正立方体呢？

3.A rectangular photograph is surrounded by a border that is 1 inch wide on each side.  The total area of the photograph and the border is M square inches.  If the border had been 2 inches wide on each side, the total area would have been (M + 52) square inches.  What is the perimeter of the photograph, in inches?

 

D.     40

三个白痴问题，3X～～～～～

sammy生米

以下是引用flyingjune在2007-3-25 16:52:00的发言：

1.Six cards numbered from 1 to 6 are placed in an empty bowl.  First one card is drawn and then put back into the bowl; then a second card is drawn.  If the cards are drawn at random and if the sum of the numbers on the cards is 8, what is the probability that one of the two cards drawn is numbered 5 ?

答案是2/5，而我做出来却变成了1/3 －－！！

答案是2/5，而我做出来却变成了1/3 －－！！

2,6
3,5
4,4
5,3
6,2
和是8的只有上述5种情况，2张card中有1张是5的有2种，所以2/5

2.cube是不是就一定是指正立方体呢？

立方也是用cube表示

3.A rectangular photograph is surrounded by a border that is 1 inch wide on each side.  The total area of the photograph and the border is M square inches.  If the border had been 2 inches wide on each side, the total area would have been (M + 52) square inches.  What is the perimeter of the photograph, in inches?

D.     40

你的解题思路和过程？你是怎样列式的？

三个白痴问题，3X～～～～～

[此贴子已经被作者于2007-3-25 21:38:55编辑过]