Brain teaser M year N day?

September 1 June and December are excluded first. If Xiao Qiang knew that it was No. 7 or No. 2, then he didn't need Xiao Ming to deduce it. Since Xiao Ming said that Xiao Qiang definitely didn't know, then it wasn't June and December.

Left, Xiao Qiang knows from Xiao Ming's words that it is not June and December, then: Assuming he knows n=5, then he still can't know the m value. So the exclusion and Suppose Xiao Qiang knows n=4, then Xiao Qiang knows that it is, but Xiao Ming only knows that m is 3, he still can't infer because it may be or only the last one is left Think about it, if Xiao Ming knows that it is September, then according to the exclusion date, there is only 1 choice left in September, isn't the answer out? Wish.

The answer should be September 1. 1) First of all, the 10 sets of dates are analyzed, and it is not difficult to find that only the two sets of dates, June 7 and December 2, have unique number of days. From this, it can be seen that if Xiaoqiang knows that n is 7 or 2, then he must know the teacher's birthday.

2) Re-analyze "Xiao Ming said: If I don't know, Xiao Qiang definitely doesn't know", and the number of months of the 10 groups of dates is 3, 6, 9, and 12 respectively, and there are more than two sets of dates in the corresponding month, so it is impossible for Xiao Ming to know the teacher's birthday after learning about m. 3) Further analysis," Xiao Ming said

If I don't know, Xiaoqiang definitely won't know", combined with the conclusion of Step 2, it can be seen that Xiaoqiang will never know after learning n. 4) Combining steps 3 and 1, it can be inferred that all the dates of June and December are not the teacher's birthday, because if Xiao Ming knows that m is 6, and if Xiao Qiang's n==7, then Xiao Qiang knows the teacher's birthday.

In the same way, if Xiao Ming's m==12 and Xiao Qiang's n==2, then Xiao Qiang can also know the teacher's birthday. That is: m is not equal to 6 and 9.

Now there are only five sets of dates left: "March 4th, March 5th, March 8th, September 1st, and September 5th". And Xiaoqiang knows, so n is not equal to 5 (there are March 5 and September 5), at this time, Xiaoqiang's n (1,4,8) Note: Although n has three possibilities at this time, as long as Xiaoqiang knows one of them, he will draw conclusions.

So there is "Xiao Qiang said: I didn't know it originally, but now I know", for us, we still need to continue reasoning At this point, the rest may be "March 4, March 8, September 1" 5) Analyze "Xiao Ming said: Oh, then I also know", indicating m==9, n==1, (n==5 has been excluded, there are two groups in March).