Got a test tomorrow on this stuff. If I know how to attack these problems, I will be ok.

1. A water plant treats a flow of 9.0 ML/d. the Mix chamber is 0.75m x 0.75m and the depth of water is 1.0m. Flocculation basin is 15m x 5m x 2.5m. What is the flocculation time in minutes?

3. The Attempt at a Solution :
9.0ML/d = 375kl/h
15 x 5 x 2.5 = 187.5m^3 = 187 000 L
.75x.75x1 = .56m^3 = 560 L

I'd write down what I actually did, but it is nowhere even close. I keep getting numbers much less or wayyyyyy higher.

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1. the Chlorine demand of a certain water is 3.0mg/L. If the plant operator adds 40lb's of chlorine gas to treat 1.0 million gallons of water, what should be the chlorine residual in mg/L?

2. My attempt
I thought I was right, I still think I am. It says the answers is 1.8 but it just doesn't seem right to me.

CONVERSIONS:
1 000 000 gallons --> 3 785 411.78 L
40 lb ---> 18. 143 kg ----> 18 143 000 mg

18 143 000mg/3 785 411.78 L = 4.79mg/L

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3. A storage reservoir is 12m wide and 16m high. What is pressure at the bottom of the reservoir, when it is half full?

my attempt
i got it right, but somehow i think it was a fluke.

16m/2 = 8m
8m x 9.81 = 78.9 = 80 kPa(final answer)

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4. you are required to provide a 2.5mg/L chlorine dosage to water pumped from a well at a rate of 35L/s/ On the well site, you have 200L capacity hypochlorite tank containing 12% chlorine solution. If the feed pump is properly calibrated, how many litres of chemical should be used per hour?

my attempt
Not even worth showing you guys. It is so wrong it is funny. I get a massively high number. The final correct answer is 2.6

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5. What is the metres of head at the discharge side of the pump that is pumping at a pressure of 93psi?

my attempt
93 x 9.81 = 912 <----- so wrong. answer is actually 65.
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I realize for alot of people these questions are simple. For me, I haven't done this stuff in years and I really don't know how to act these 5 types of problems. However, on the test, these are the types of questions I will get. So if I know how to attack them I will be ok. I hope you people can help me out! Thanks alot