Let's roll up our sleeves and solve this. We have 501 and we're going to multiply it by 20, essentially adding 501 to itself 20 times.
Step 1: 0 + 501 = 501
Step 2: 501 + 501 = 1002
Step 3: 1002 + 501 = 1503
Step 4: 1503 + 501 = 2004
Step 5: 2004 + 501 = 2505
Step 6: 2505 + 501 = 3006
Step 7: 3006 + 501 = 3507
Step 8: 3507 + 501 = 4008
Step 9: 4008 + 501 = 4509
Step 10: 4509 + 501 = 5010
Step 11: 5010 + 501 = 5511
Step 12: 5511 + 501 = 6012
Step 13: 6012 + 501 = 6513
Step 14: 6513 + 501 = 7014
Step 15: 7014 + 501 = 7515
Step 16: 7515 + 501 = 8016
Step 17: 8016 + 501 = 8517
Step 18: 8517 + 501 = 9018
Step 19: 9018 + 501 = 9519
Step 20: 9519 + 501 = 10020

So, 501*20 = 10020