Đáp án:
`(1- 1/4) × (1 - 1/9) × (1 - 1/25) × (1 - 1/36) × (1-1/49)`
`= 3/4 × 8/9 × 24/25 × 35/36 × 48/49`
`= (3 × 8 × 24 × 35 × 48)/(4 × 9 × 25 × 36 × 49)`
`= (3 × 4 × 2 × 8 × 3 × 5 × 7 × 8 × 6)/(4 × 3 × 3 × 5 × 5 × 2 × 3 × 6 × 7 × 7)`
`= ( 8 × 8 )/( 5 × 3 × 7)`
`= 64/105`