`( 1-1/2 ) × ( 1- 1/3 ) × ( 1-1/4 ) × ( 1- 1/5 ) × ... × (1- 1/2003) × (1- 1/2004 )`
`= (2/2-1/2)×(3/3-1/3)×(4/4-1/4)×(5/5- 1/5)× ... ×(2003/2003-1/2003)×(2004/2004-1/2004 )`
`= 1/2 × 2/3 × ... × 2002/2003 × 2003/2004`
`= {1 × 2 × ... × 2002 × 2003}/{2 × 3 × ... × 2002 × 2003 × 2004}`
`= 1/2004`
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