Find all factor pairs for a whole number in the range 1-100. Recognize that a whole number is a multiple of each of its factors. Determine whether a given whole number in the range 1-100 is a multiple of a given one-digit number. Determine whether a given whole number in the range 1-100 is prime or composite.
Identify factor pairs for any number 1-100. For example, 3 and 6 is a factor pair of 18 while 2 and 4 is not. After that, teach students how to solve Shikaku puzzles, then give your students some puzzles to solve. Puzzles of various difficulty are conveniently organized here. Additionally, here are some random Shikaku puzzles I've stumbled across. After your finished with Shikaku, explore the game found here and here. After that, give your students this challenge. Before attempting the challenge, students must be able to multiply two-digit numbers by two-digit numbers. They don't need to know the divisibility rule for 13, despite the name of the problem. Conclude by leading the investigations found here, here, and here. Two more instances of the Tax Collector game being played can be seen here. Also, go to this page and give the puzzles found on the slides Hungry Monsters and Hungry Monsters Pt. 2.
Notes: At this point, 4th graders don’t know the divisibility tests, so without this or the sieve of Eratosthenes, there’s no way they can test primality.