bunch of Math question

[Ferdowsi]

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first of all, How do you calculate this trig: COS(pi+301pi/2)

then I'm confused about this mixture problems.

Q1. A chemical which is 15% conentrate was mixed with 2 liter of Water to make a 12% concentrate what wasthe initial HCL volume in the mixture?

Q2A chemist needs a solution of tannic acid 70% pure. How much distilled water must he add to 5 gallons of acid which was 90% pure to obtain the 70% solution?


so I know the general strategy for these kind of question but my question is why on the second question water percentage of water is 0 and for the frist one is 85%? I don't get it🙄😱

 

[Ferdowsi]

anyone?

 

[WhyMD]

Q1. is the answer 1.2L of the chemical and 8L of solution?

Q2. is the answer about 1.4 gallon?

 

[Streetwolf]

first of all, How do you calculate this trig: COS(pi+301pi/2)

then I'm confused about this mixture problems.

Q1. A chemical which is 15% conentrate was mixed with 2 liter of Water to make a 12% concentrate what wasthe initial HCL volume in the mixture?

Q2A chemist needs a solution of tannic acid 70% pure. How much distilled water must he add to 5 gallons of acid which was 90% pure to obtain the 70% solution?


so I know the general strategy for these kind of question but my question is why on the second question water percentage of water is 0 and for the frist one is 85%? I don't get it🙄😱

Q1: It isn't 10% water? Cause the original acid solution is 90% pure which means there's 90% acid and 10% water.

Q2: There's 15% concentrate which means 15% HCl and 85% water.

Trig question: Remember that trig functions cycle every 2pi. So cos(2pi) = cos(4pi) = cos(6pi) = cos(300pi). What you have there is really cos(pi + 300pi/2 + pi/2) = cos(pi + pi/2) = cos(3pi/2). I can take the 300pi/2 out because that's the same as 150pi, which is 75(2pi). Since every 2pi is the same value, those can drop out.

 

[Ferdowsi]

Q1. is the answer 1.2L of the chemical and 8L of solution?

Q2. is the answer about 1.4 gallon?

yup but why.. i don't get it..why on second question water percentage is considered zero but on first question is 85%...