Alright, let's solve this math problem step by step. First, we have the number 20. Next, we see the multiplication sign, which means we need to multiply something. And what are we multiplying it by? We multiply it by 20. So, we're going to take the number 20 and add it to itself 20 times.
Step 1: 0 + 20 = 20
Step 2: 20 + 20 = 40
Step 3: 40 + 20 = 60
Step 4: 60 + 20 = 80
Step 5: 80 + 20 = 100
Step 6: 100 + 20 = 120
Step 7: 120 + 20 = 140
Step 8: 140 + 20 = 160
Step 9: 160 + 20 = 180
Step 10: 180 + 20 = 200
Step 11: 200 + 20 = 220
Step 12: 220 + 20 = 240
Step 13: 240 + 20 = 260
Step 14: 260 + 20 = 280
Step 15: 280 + 20 = 300
Step 16: 300 + 20 = 320
Step 17: 320 + 20 = 340
Step 18: 340 + 20 = 360
Step 19: 360 + 20 = 380
Step 20: 380 + 20 = 400

So, 20*20 = 400