“What are the strongest days of the week?”/“Saturday and Sunday. The rest are weekdays.”

A riddle about the days of the week has been cited in print since at least 1855:
 
Q: What is the strongest day of the week?
A: Sunday. All of the rest are “weak” days.
 
Saturday later joined Sunday as part of the weekend. A riddle was printed in newspapers in 1973:
 
Q: What are the two strongest days of the week?
A: Saturday and Sundays. Because the other days are week days.
 
“Do you guys remember when I told you about my spine issue? It was about a week back” is another “week”/“weak” pun.
     
       
Chronicling America
21 June 1855, Eaton (OH) Democrat, pg. 1, col. 5:
The question was asked the other day, “Which day of the week was the strongest?” Sunday, is the answer, as all the rest are weak days.
 
Chronicling America
21 February 1866, Lewistown (PA) Gazette, pg. 1, col. 6:
Which is the strongest day in the week? Sunday, because all the rest are weak-days.
     
Google Books
Eli Perkins (at Large):
His Sayings and Doings
By Melville De Lancey Landon
New York, NY: J. B. Ford & Company
1875
Pg. 71:
“By the way, Miss Julia, do you know which is the strongest day in the week?” I asked modestly, taking her beautiful gold fan.
 
“No. Which is the strongest day, Mr. Perkins?”
 
“Why, Sunday, Julia; don’t you know all the other days are weak days!
 
7 June 1884, The Saturday Evening Post (Philaelphia, PA), “Facetiae,” pg. 15, col. 1:
Which is the strongest day in the week? Sunday—because all the rest are weak days.
 
19 November 1908, Richmond (IN) Palladium and Sun-Telegram, “Riddles,” pg. 8, col. 3:
Which is the strongest day in the week? Sunday, because all the rest are weak days.
 
7 June 1924, Richmond (IN) Palladium and Sun-Telegram, pg. 10, col. 2:
Randy Riddle Says—
Why is Sunday the strongest day in the week?
Col. 4:
Answer to today’s riddle: Sunday is the strongest day because all the rest are weak days.
 
2 September 1965, Kokomo (IN) Tribune, “Hello There!” by Beverly Abner, pg. 10, col. 5:
OUT O’ THE MOUTHS O’ BABES—“Sunday is the strongest day of the week. The rest are weak days.”
 
20 January 1973, The Clarion-Ledger (Jackson, MS), “Mini-Jokes,” The Mini Page, pg. 3, col. 1:
Q. What are the two strongest days of the week?
A. Saturday and Sundays. Because the other days are week days.
Gaye Mitchell
Carriere
 
22 November 1977, Gazette Telegraph (Colorado Springs, CO), “Shari Lewis’ Kids-Only Club,” pg. 8-A, col. 6:
Yesterday’s Brain Twister: What are the strongest days of the week?
Answer: Saturdays and Sundays—the rest of them are “weak” days.
 
Google Books
30 July 1979, New York magazine, pg. 42, col. 1:
Sample: “Why are Saturday and Sunday the strongest days? (pause) Because all the rest are weak days (canned robot laughter).”
 
12 June 1988, The News Journal (Wilmington, DE), “Just for Laughs,” Pennywhistle Press, pg. 4, col. 5:
Question: What are the strongest days in the week?
Answer: Saturday and Sunday—the rest are weekdays.
Terri McAfee Age 10 1/2
Cleveland, Oklahoma
 
13 April 1999, Los Angeles (CA) Times, “The Kids’ Reading Room; Pint-Sized Punch Lines,” pg. E10, col. 4:
What days are the strongest days of the week? Saturday and Sunday—the others are just weak days. (Rachel, 11, Seal Beach, Hopkinson Elementary)
   
Twitter
Nick
‏@nickdefa
What are the strongest days of the week?
Saturday& Sunday, The rest are weak-days!
3:52 PM - 23 Nov 2008
 
Twitter
The Sir
‏@SirStinson
What are the strongest days of the week?
Saturday and Sunday. The rest are “week"days!
3:16 PM - 3 Apr 2009
 
Google Books
Just Jokes a Collection of Kids Jokes
By Phyllis Agles-Johnson
Lulu Publishing (Lulu.com)
2010
Pg. 49:
Q. What are the strongest days of the week?
A. Saturday & Sunday, The rest are week (weak) days!
 
Reddit—Jokes
What are the strongest days of the week?
submitted January 19, 2017 by jessicaho656
Saturday and Sunday. The rest are weekdays.