Hi... sorry my post is so late... i was just reading this now. I also got Thursday, but thought I would mention my reasoning behind it.
If he's learning positive and negative numbers (or if not, then it's an opportunity to introduce it), you can call truth (+) and lying (-). So if you're looking for the day when they are lying it's (+)(-)=(-). [If you were looking for the day when they were telling the truth, it's (+)(+)=(+) or (-)(-)=(+).]
Then set up 2 columns and 2 rows (columns are + and - for days telling the truth and days lying), rows are for each person. Add the days of the week (M, T, W, Th, etc) into each of the 4 boxes based on the problem. Then look for the day (Thursday) when you can pick the following day (Friday) and have it be in the opposite column for each person.
Does that make sense? Hope it helps
That chart problem is a logic based reasoning problem as well as a sequential problem. You would use the draw a picture strategy to solve that problem.
