Number Bonds take students beyond just practicing math facts. They illustrate the relationships between numbers as well as the inverse relationship between basic operations of addition-subtraction or multiplication-division. Students work with these 5" x 5" Write-On Wipe-Off activity cards to build fluency, and gain number sense at the same time. Teachers can use the cards with groups, in pairs or with individuals. Problems can be written with dry erase markers on cards. Students can answer problems and hold up card for formative assessment by teacher or other students. 30 Write-On Wipe-Off cards in set.