Earth Day Math Activities - Problem Solving Games, Math Riddles, & More! 2nd Grade | 3rd Grade | 4th Grade | Homeschool This Earth Day-themed math activity unit includes 4 versions of math riddles featuring addition, subtraction, multiplication, or division skills. Select the operation to best meet the needs of your students. A partner game activity includes practice with either multiplication or addition facts. The multiplication version allows students to use the associative property in mu