1999 – 2000 + 2999 – 3000 + 3999 – 4000 + 4999 – 5000 + 5999 – 1000

1999 – 2000 + 2999 – 3000 + 3999 – 4000 + 4999 – 5000 + 5999 – 1000

= (2999 – 2000) + (3999 – 3000) + (4999 – 4000) + (5999 – 5000) + (1999 – 1000)

= 999 + 999 + 999 + 999 + 999

= 999 × 5

= 4995