【HaiChuan: Using your brain keeps you young】Guess what the birthday is
Thread Content
Xiao Ming and Xiao Qiang are both students of Teacher Zhang. Teacher Zhang’s birthday is on the Mth day of the Nth month. Both of them know that Teacher Zhang’s birthday falls on one of the following ten dates. Teacher Zhang told Xiao Ming the value of M and told Xiao Qiang the value of N: March 4th, March 5th, March 8th, June 4th, June 7th, September 1st, September 5th, December 1st, December 2nd. Xiao Ming said, \"If I don’t know it, then Xiao Qiang definitely doesn’t know it either.\" ； Xiao Qiang said: I didn’t know before, but now I do ； Xiao Ming said, Oh, then I know it too. Please infer from the above conversation what Zhang’s teacher’s birthday is
Just a random guess; it’s different from the one above
Baidu Shangxue*. You’re missing December 8th; it’s simpler that way.
If the N values are 2 and 7, which have no repeating values, then Xiao Qiang can immediately know which day it is; therefore, June 7th and December 2nd can be excluded； Xiao Ming said: If I don’t know it, then Xiao Qiang definitely doesn’t know it either. This means that Xiao Ming knows that Xiao Qiang’s N value is not two or seven; therefore, Xiao Ming’s M value cannot be six or twelve ； Xiao Qiang said: I didn’t know it before, but now I do. This means that within the remaining days, the N values are not repeated; it’s not five ； Now only March 4th, March 8th, and September 1st are left ； Xiaoming said, Oh, then I get it too; it means that the M values won’t repeat either in the remaining days, and only September 1st is left