Open Middle®
Directions: Using the digits 1 through 9, once each, fill in the blanks so that the statement is true.
Hint
Write down the formulas for nCr and nPr and try a few guesses!
Answer
6C3 = 5P2, 6C1 = 3P2, 6C5 = 3P2
Source: Mark Alvaro and Kerri Swails
At most once each?
4C2 = 6P1
9C1=9P1