Math is all around us, and it's nice to have a gut-level check on whether or not something makes sense. Say you're at a restaurant, and you and your other both

Math is all around us, and it's nice to have a gut-level check on whether or not something makes sense. Say you're at a restaurant, and you and your other both ordered $25-ish dollar entrees, and $10-ish drinks, and split a $15-ish appetizer, and the bill comes closer to $150 than $100, something was probably mixed up. That kind of quick approximation gives you a nudge to check real numbers.