1) Albert knows Bernard cannot know the answer immediately. As 18 and 19 are days that only appear once, the month must not contain those dates, so May and June are eliminated.
2)Bernard is able to identify the month based on knowing it can't be june or may and based on his date. Therefore Bernard cannot have had the number 14. He must have 15,16, or 17.
3) Knowing it is 15, 16, or 17 uniquely identifies the date for albert. Since august has 2 options left, it must be july, and the only date available is July 16.
This is a tricky problem, but it is one that is fairly straightforward to approach step by step. Definitely appropriate for advanced students at age 15. The problem reminds me of the question about how many people on an island have blue/brown eyes.
I haven't done logic problems in a long time, so I may have erred and would welcome alternative interpretations.
The island puzzle, for those who haven't seen it yet.
I think that one is much more difficult because the problem is stated in a way that makes the readers think she has much less information that is actually given. The birthday problem has no trick phrasing in it.
Well, maybe a little tricky. You'd get stuck if you tried to reason from four months and six days. This would be a likely mistake if the problem were read aloud with the list of dates as "May 15, 16, and 19, or June 17 and 18..."
Recognizing that Albert and Bernard are both working with sets of 10 elements each -- one for each possible date -- then it becomes a simple graph problem.
Write a chart with rows labeled months and columns labeled days. Put a mark on each possible date. Albert circles one row and Bernard one column. Albert says none of the marks in his rows are the only marks in their columns, so draw a line through the columns with only one mark and the rows that intersect at that mark. Bernard says there is only one mark in his column after eliminating the row, so draw a line through the columns with more than one mark. Albert says there is only one mark in his row, so draw a line through the row that still has two marks in it. The only one left is July 15.
I am not sure that is true. If albert knows bernard doesn't know the day at the beginning, it can't be june since the number 18 would be uniquely identifiable as june 18 for bernard from the beginning.
The biggest concern for me actually is that in making this move, amazon is putting itself in direct competition with libraries' ebook/audiobook lending services. Many of those even use the kindle network!
Will amazon continue to allow books to reach those services as soon after release? Do they have the power to stop it in the first place? I think it will be interesting to see how the company, which it is clear has a lot of leverage in the book publishing community, handles competing with a free alternative.
1) Albert knows Bernard cannot know the answer immediately. As 18 and 19 are days that only appear once, the month must not contain those dates, so May and June are eliminated.
2)Bernard is able to identify the month based on knowing it can't be june or may and based on his date. Therefore Bernard cannot have had the number 14. He must have 15,16, or 17.
3) Knowing it is 15, 16, or 17 uniquely identifies the date for albert. Since august has 2 options left, it must be july, and the only date available is July 16.
This is a tricky problem, but it is one that is fairly straightforward to approach step by step. Definitely appropriate for advanced students at age 15. The problem reminds me of the question about how many people on an island have blue/brown eyes.
I haven't done logic problems in a long time, so I may have erred and would welcome alternative interpretations.