Comedy adventure series, aimed at four- and five-year-olds, in which animated numbers solve mathematical problems in the real world, with input from real children. Number 6 is preparing to play an estimating game on the Thinkyjump machine. He is joined by 3 but their game is interrupted by a call from Agents. A boy is building a meccano model - but the pieces have taken on a life of their own. Number 5 takes on the mission and heads out to help. She discovers the Problem Blob causing trouble all over the place. A builder's nails are moving by themselves and an entertainer's modelling balloons are out of control, not to mention a class of children misbehaving for a teacher. The Numberjacks realise that they have to estimate the number of things to sort the problem out. Brain Gain helps and they manage to defeat the Problem Blob.