“What’s the longest piece of furniture in the school?”/“The multiplication table.”

A school riddle is:
 
Q: What’s the longest piece of furniture in the school?
A: The multiplication table.
 
The joke has been cited in print since at least 1957.
 
       
Google Books
The Year-Round Party Book
By William Playford Young and Horace J Gardner
Philadelphia, PA: Lippincott
1957
Pg. 7:
What is the longest piece of furniture? The multiplication table.
 
Google Books
Jokes, Puns, and Riddles
By David Allen Clark
Illustrated by Lionel Kalish
Garden City, NY: Doubleday
1968
Pg. 160:
Question: What’s the longest piece of furniture in the world?
Answer: The multiplication table.
 
30 September 1974. Indianapolis (IN) News, “Mini Jokes,” The Mini Page, pg. 3, col. 1:
Q. What’s the longest piece of furniture in the world?
A. The multiplication table.
—James Wallace, Indianapolis
 
Google Books
July 1983, Boys’ Life, “Think & Grin,” pg. 74, col. 2:
Mabel: What is the longest piece of furniture in the world?
Abel: I don’t know. What?
Mabel: The multiplication table. — Francois Antebi, Greenwich, Conn.
 
Twitter
Daily Joker‏
@DailyJokePost
Whats the longest piece of furniture in the
school? The multiplication table. http://dailyjokepost.com/492
6:00 AM - 24 Aug 2009
 
Google Books
Best Ever Classroom Jokes:
Because some of us never grow up
By Mike Haskins
London, UK: Pavilion Books
2015
Pg. ?:
What’s the longest piece of furniture in the world?
The multiplication table.
 
Twitter
S.Rippetoe ⤵‏
@S_Rippetoe
What’s the longest piece of furniture in the school? The multiplication table.
7:00 PM - 27 Jun 2017