Daisy bought A new speaker that was marked at $90.15. When she got to the register, she learned that the speaker was marked down 25%. How much money did she save?

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step-by-step explanation:

a is the right answer

make sure you have version 2.50

try looking in the very back of the book : )

step-by-step explanation:

you can download it here

ending amount = beginning amount / (2^n)

where "n" = number of half-lives (or elapsed time / half-life)

ending amount = 50 mg / (2 ^10 / 5.3)

ending amount = 50 mg / (2 ^ 1.8867924528)

ending amount = 50 m / 3.6981210597

ending amount = 13.5203794557 mg

or about 13.5 mg remain

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