Learning Resources Hot Dots Maths More Subtraction Practice Cards. This set provides self-checking practice activities children master on their own! Young learners simply touch the interactive pen to a Hot Dot and the Talking Hot Dots Pen responds instantly with a green light and positive sounds. Incorrect answers receive a red light and gentle wrong sound or phrase. Set covers subtraction facts 13-19 and includes 50 double sided cards conveniently stored in a plastic storage case. Requires Learning Resources Talking Hot Dots pen (available separately).