Started with sequences. Arithmetic and Geometric. Looked at the relevant formulas then used them.
He needed to figure out whether series were arithmetic or geometric.
And looked at convergence for geometric series.
Also looked at permutations and combinations. Permutations are like a telephone number, the order matters. With combinations, they are more like pizza toppings- mushrooms and olives is like olives and mushrooms, the order does not matter.
Many calculators can compute these.