F.U.N.? stands for Fluency & Understanding Numbers. In Fourth and Fifth Grade, the F.U.N.? Empty Number Line can be a great tool for students for visualizing operations, fractions and decimals, magnitude of numbers, place value, as well as many other concepts. Includes number line hardware, activity guide and 481 cards specific to the Common Core Standards for Grades 4-5, and 30 blank write-on/wipe-off cards.