My dad made us learn that. In college, I would give the answer almost immediately and the professor would wait for someone with a calculator to finish typing it in and then look amazed when I had been right.
When we homeschooled, I did not allow my kids to use calculators until they were in about 7th grade and doing algebra problems where doing the math long hand was too time consuming.
But by then, they had demonstrated a proficiency for being able to do math in their heads and the same thing would happen, they’d mentally calculate an answer in half the time it took the public educated kids to enter the problem into their calculators, not to mention the additional time they spend arguing over who had the right answer because most of them got different answers.