Open Middle®
Directions: Using the digits 0 to 9, at most one time each, place a digit in each box to make the largest/smallest possible sum.
Hint
How does the relationship between the upper limit and the multiplier of n affect the sum?
Answer
For maximum, the answer is an upper limit of 5, a lower limit of 2, and a multiplier of 7 to get 98.
For minimum, the answer is an upper limit of 2, a lower limit of 1, and a multiplier of 3 to get 09.
Source: Owen Kaplinsky