Jacob is conducting a study in which he teaches children with adhd how a new technique for how to multiple numbers. on day one, he teaches them how to multiply by two (1 x 2, 2 x 2, 3 x 2 on day two, he teaches them how to multiply by three (1 x 3, 2 x 3, 3 x 3 over time, the kids are quick to grasp the concepts, so the time he needs to teach them how to multiply on day 10 is much shorter than the time he needed to teach them on day one. excited, he concludes that his new technique can children with adhd learn to multiply even large numbers, like 11 x 13 from the very start of their lessons. what external validity confound did jacob not take into account?