Let's get this math done. We have 820 and we're going to multiply it by 5. This is the same as taking 820 and adding it to itself 5 times.
Step 1: 0 + 820 = 820
Step 2: 820 + 820 = 1640
Step 3: 1640 + 820 = 2460
Step 4: 2460 + 820 = 3280
Step 5: 3280 + 820 = 4100

So, 820*5 = 4100