This logic grid puzzle can be solved by using the clues to eliminate answers. One possible solving path is:
- By clue 2, neither Angelina nor Lucille had the murder mystery or tropical getaway parties, none of those four parties were either in August or on the 1st, and August must be the 1st.
- By the sixth clue, Deborah’s birthday must be May 25, June 4, June 9, or June 16. Since her birthday never falls on Memorial Day by the first clue, her birthday must be one of the three June dates.
- According to clue 8, the pony party was two months before the tropical getaway party. Since the tropical getaway party wasn’t in August, the two parties were either May and July or July and September. Either way, none of the other three parties can take place in July, and neither party was for Deborah.
- The first clue further eliminates both July and September from being on the 4th.
- Since the June party was later in the month than the July party according to clue 4, and we already know that the July party is on the 9th or later and the June party is not on the 25th, the June party must be on the 16th, and the July party is on the 9th. This means the May party is on the 4th and the September party is on the 25th. Thanks to clue five, we know that the May 4 party is the basketball party.
- This leaves the pony party as the July party, with the tropical getaway party in September. From this, the murder mystery party is placed in June, with the Regency era party in August. With this, the three lower grids are complete, and all the information for Deborah is known.
- The eighth clue now tells us that Lucille cannot have had the party in May or September. Thus, she had the pony party on July 9th.
- Angelina can only have had the basketball or Regency era birthday parties. However, since the Regency era party was in August, she must have had the basketball party on May 4.
- By clue three, Florence must have had the August 1 Regency era party, and Isabelle had the September 25th tropical getaway party.
This gives the following grid:
Reading the letters in the correct squares in order by column gives the phrase FOR ISABELLE WHAT IS THE BIRTHSTONE? Since Isabelle was born in September, her birthstone is SAPPHIRE.