Alright, let's work through 2501 times 820 step by step
2501 × 820 = 820 × (2501)
+ 820 × 1 giving us 820
+ 820 × 00 that equals 0
+ 820 × 500 what gives us 410000
+ 820 × 2000 producing 1640000

= 2050820
