When working with formulas involving Pi, sometimes it's easier to just leave the answer in terms of Pi. Othertimes, when needing a specific value for volume or area of a sphere, circle, cylinder for example, it's best to use 3.14 or 22/7 as approximations for Pi. Yes, many people have memorized Pi to a ridiculous number of digits, but for all practical purposes, a few decimal points of Pi will suffice.