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A glass was filled with 10 ounces of water, and 0.01 ounce of the water evaporated each day during a 20-day period. What percent of the original amount of water evaporated during this period?

I came to a conclusion that it would 20 days * 0.01 ounce/day = 0.2 ounce for 20 days. And to get the % evaporated it would be 0.2 * 100% which is 20% . But the answer is 2%, I am unable to understand why would it be 2%?

Thank you!

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2 Answers 2

20 days * 0.01 ounce/day = 0.2 ounce for 20 days

is correct.

For the fraction evaporated you need to divide the amount evaporated by the starting amount: $\dfrac{0.2 \text{ ounces}}{10 \text{ ounces}} = 0.02$. If you do not divide by something in ounces or something similar then you will be left with ounces in the units of the answer.

You then multiply this by one hundred to get a percentage: $0.02 \times 100\% = 2\%$.

Or you could combine the last two steps into one: $\dfrac{0.2 \text{ ounces}}{10 \text{ ounces}}\times 100\% = 2\%$.

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I don't know why you did $0.2*100\%$. The correct approach is to divide, $0.2$ divided by $10$, giving $.02$, and then express that number as a percentage, that is, as something out of 100. Well, $.02=2/100$, so it's 2 percent.

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