Directions: Using the digits 1 to 9 at most one time each, fill in the boxes to make the smallest (or largest) difference. Source: Robert Kaplinsky

Directions: Using the digits 1 to 9 at most one time each, fill in the boxes to make the smallest (or largest) sum. Source: Robert Kaplinsky

Directions: Using the digits 0 to 9 at most one time each, place a digit in each box to make the equality true. Source: Graeme Lachance

Directions: Using the integers -9 to 9 at most one time fill in the boxes to create a right triangle on the coordinate plane. Source: Tracy Conte

Directions: Using the digits 0 through 9 at most one time, place a digit in each box to make a true equation. Source: Ellen Metzger

Directions: Using the digits 1 to 9 at most once each, fill in the boxes to make a true statement. Source: Robert Millett

Directions: Using the digits from 1 to 9, at most once, make as many true statements as possible. Source: Rochelle Telfer

Directions: Using the digits 1 through 9 fill in the blanks to make a product of 1. Source: Owen Kaplinsky

Directions: Use the digits 1 to 9, at most one time each, to fill in the boxes so that the three fractions have a product as close to 1 as possible. Source: Patrick Vennebush

Directions: Using each of the digits 0-6 only once, make two equivalent ratios (also known as a proportion). Source: AnneMarie Untalan