Marnie has already eaten 5 of the chips + 5 more = <<5+5=10>>10 chips Marnie ate.
The bag has 100 chips in it and Marnie has only eaten 10, 100 - 10 = <<100-10=90>>90 chips left.
If Marnie eats 10 chips a day starting from the second day she has them, it will take her 90 chips in the bag / 10 chips Marine eats a day = <<90/10=9>>9 days to eat the whole bag.
However, Marnie also ate chips on the first day she bought them, so 9 + 1 = <<9+1=10>>10 days to eat the whole bag.
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