5÷(1-
)÷(1-1 2
)÷(1-1 3
)÷(1-1 4
)÷(1-1 5
)÷(1-1 6
)÷(1-1 7
)÷(1-1 8
),1 9
=5÷
÷1 2
÷2 3
3 4
÷4 5
÷5 6
÷6 7
÷7 8
,8 9
=5×2×
×3 2
×4 3
×5 4
×6 5
×7 6
×8 7
,9 8
=45(千克),
答:这袋大米原来有45千克.
故答案为:45.