This reminds me of Case Interview Math: https://www.caseinterview.com/math/home.php https://www.caseinterview.com/math/home.php Try with "Estimation Math", "Ra

This reminds me of Case Interview Math: https://www.caseinterview.com/math/home.php https://www.caseinterview.com/math/home.php Try with "Estimation Math", "Random", and "Hard". A friend of mine told me about this website. He used it to practice for interviews. I took it as a game. It's less about precision and more about "close enough" but quick calculations. After a while, you learn to focus on the most critical part of each question, which depends upon the operator and the number of digits, and dismiss what's irrelevant.