How Much Pure Disinfectant is Needed to Increase Solution Strength by 25%?

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Discussion Overview

The discussion revolves around determining the amount of pure disinfectant needed to increase the strength of a 30-gallon solution from 8% to a higher concentration, specifically by 25%. Participants engage in formulating and solving the associated mixture problem, exploring different interpretations of the problem statement.

Discussion Character

  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant proposes an initial equation based on the assumption that the final concentration should be 25% of the total volume, leading to the equation 0.08(30) + x = 0.25(x + 100).
  • Another participant corrects the interpretation, suggesting that the concentration should increase to 10% (1.25 times the original 8%), leading to the equation 0.08(30) + x = 0.1(x + 30).
  • Subsequent calculations by participants lead to different values for x, with one participant concluding x = 6, while another arrives at x = 0.66, indicating discrepancies in the arithmetic steps.
  • Participants point out errors in the algebraic manipulation of the equations, particularly in how terms are moved between sides of the equation.
  • There is a discussion about rounding the final answer, with one participant noting that x could be approximated to 0.67 gallons or expressed as 2/3 gallons.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct amount of pure disinfectant needed, as different interpretations and calculations lead to varying results. The discussion remains unresolved regarding the correct approach and final answer.

Contextual Notes

There are unresolved mathematical steps and potential misinterpretations of the problem statement that affect the calculations presented. The dependence on precise definitions of terms like "increase by 25%" is also a point of contention.

mathdad
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How much pure disinfectant must be added to 30 gallons of an 8% solution to increase its strength by 25%?

Let x = pure disinfectant to be added

The word PURE tells me that 100 will be in the equation somewhere.

30 gallons of 8 percent = 0.08(30)

Must be added to some unknown = plus x

My equation is 0.08(30) + x = 0.25(x + 100)

Correct? If not, can someone break this mixture problem step by step leading to the right equation?
 
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The LHS of your equation is correct, however for the RHS, we want the concentration to be increase BY 25%, not TO 25%, which means instead of 8%, we want 1.25*8% = 10%. Also, the amount of the final solution will be x + 30, not x + 100...so the correct equation, at least for the way I am interpreting the problem, is:

0.08(30) + x = 0.1(x + 30)
 
0.08(30) + x = 0.1(x + 30)

2.4 + x = 0.1x + 3

x - 0.1x = 2.4 + 3

0.9x = 5.4

x = 5.4/0.9

x = 6

So, 6 pure disinfectant must be added.

Correct?
 
RTCNTC said:
0.08(30) + x = 0.1(x + 30)

2.4 + x = 0.1x + 3

x - 0.1x = 2.4 + 3

You've subtracted 2.4 from the LHS, but added 2.4 to the RHS...:D
 
0.08(30) + x = 0.1(x + 30)

2.4 + x = 0.1x + 3

x - 0.1x = -2.4 + 3

0.9x = 0.6

x = 0.6/0.9

x = 0.66

Right?
 
RTCNTC said:
0.08(30) + x = 0.1(x + 30)

2.4 + x = 0.1x + 3

x - 0.1x = -2.4 + 3

0.9x = 0.6

x = 0.6/0.9

x = 0.66

Right?

If you are going to round to 2 decimal places then x ≈ 0.67 gal., otherwise x = 2/3 gal. :D

x = 0.6/0.9 = 6/9 = 2/3
 
MarkFL said:
If you are going to round to 2 decimal places then x ≈ 0.67 gal., otherwise x = 2/3 gal. :D

x = 0.6/0.9 = 6/9 = 2/3

Great as always.
 

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