For some of my activities I'm forced to estimate the number of hours I've put into them with very rounded numbers (100 hours, 30 hours, etc.) simply because I have no idea what the real number is. For some others (hobbies, traveling, sports, etc.) that I've been doing forever I have no clue what the number of hours I have would be aside from making a wild estimate. I'm afraid that adcoms will think I'm maliciously fudging my numbers when it's not my intention at all.