Alright, let's work through 1000 times 1991 step by step
1000 × 1991 = 1991 × (1000)
+ 1991 × 0 yielding 0
+ 1991 × 00 which equals 0
+ 1991 × 000 that is equal 0
+ 1991 × 1000 that is equal 1991000

= 1991000
