Master subtraction in no time with Hot Dots Math Flash Cards!nSet includes 50 double-sided cards for 100 interactive subtraction problems using numbers 13-19.nUse as basic flash cards or add the Hot Dots Talking Pen (not included) for instant reinforcement.nTouch the pen to an answer dot for positive reinforcement (correct responses) or gentle redirection (incorrect responses).nPerfect for independent, self-paced learning.nUse like regular teacher- or parent-directed flash cards, with individual students or small groups. Add the Talking Hot Dots Pen, and students can drill independently with Hot Dots instant reinforcement! Students touch the pen to the correct answer, and get a positive response. The plastic storage case makes these great send-home helpers for students needing extra reinforcement. All for about the same cost as regular flash cards! Grades 1+ / Ages 6+.