Math Puzzle of the Week

July 6, 2009

Algebra: If you add the denominator to both the numerator and denominator of 1/3, you get 4/6 which is twice the original fraction. For what fraction will this process result in a fraction 3 times the original?

From NCTM

Answer available July 13, next puzzle

Answer to math puzzle of June 29:

Algebra: The 5th term of a geometric series is 5! and the 6th term is 6! What is the 4th term?

From NCTM

Solution: Each term of a geometric series is a fixed multiple of the previous term. Since the 6th term is 6! and the 5th is 5!, the multiple is 6 (6! = 5!•6). So the 4th term is 5!÷6 = 20. (Note that 4! = 24)

For more math puzzles, check out http://www.mathpuzzle.com/, http://mathschallenge.net/, http://www.princeton.edu/~mathclub/puzzles4.html and http://mathforum.org/k12/k12puzzles/