Fluency and Number Sense through Puzzle and Play. Number Sleuth builds number sense! Students puzzle and play with numbers using essential math concepts. Students solve the problems featured on the Challenge Cards by circling the correct responses on their dry-erase Digit Card. Instructions and ideas for multiple game variations included. Ideas for whole class or small group math stations also provided. Each grade level includes 60 double-sided cards: 30 Challenge Cards and 30 Digit Cards.