Both of the guys who do the math a different way are wrong. They make it seem like they're right by adding and multiplying the math in a different way. The woman did it wrong because she multiplied 5 by 20 and 5 by 1 and added those two. Another problems that works with their math is 4 muliplied by 15 to get 24. It's really 4 by 6 but with they way they do it, it would be 15.