When professional mathematicians solve problems, do they use pen and paper or do they type directly into LaTeX?

Question

When professional mathematicians solve problems, do they type directly into LaTeX or do they solve problems using pen-and-paper? By professional mathematicians, I include those pursuing a mathematics PhD. I'm not a professional mathematician but have to use quite a bit of math for grad school, and have experimented with both approaches. Typing out is slower but I'm able to fit more formulas and other content onto a page.