A scientist begins an experiment with 20.25 milliliters of a chemical. She adds 0.75 milliliter of water to the chemical every 10 minutes, starting at 1:30 P. M. B. The scientist continues to add 0.75 milliliters every 10 minutes, rounded to the nearest whole number, what percent of the mixture of the chemical and water is made up of water at 3:40 P. M.?

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32.5 %

Explanation:

Since the scientist starts adding water at 1:30 P.M and stops at 3:40 P.M, the time elapsed is 3:40 P.M - 1:30 P.M = 2:10. So the time elapsed is 2 hours and 10 minutes = 2 × 60 minutes + 10 minutes = 120 minutes + 10 minutes = 130 minutes.

Also, the scientist adds 0.75 milliliters of water every 10 minutes. We need to find the number of times the scientists pours water in 130 minutes.

number of times = 130 min/10 min = 13 times

So, the total volume of water added after 130 minutes or 13 times is 0.75 ml × 130 min/10 min = 0.75 ml × 13 = 9.75 ml

Now, the total volume of water and chemical is thus 9.75 ml + 20.25 ml = 30 ml.

So, the percentage of water in the mixture by 3:40 P.M = volume of water/total volume of mixture × 100 %

= 9.75 ml/30 ml × 100 %

= 0.325 × 100 %

= 32.5 %

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