Another work to paint house problem

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Discussion Overview

The discussion revolves around a problem involving two individuals, Clarissa and Shawna, who are painting a house together. The focus is on determining how long it will take Clarissa to complete the job by herself, given that they can finish the task together in 6 days and that Clarissa takes 5 days less than Shawna to complete the job alone. The conversation includes mathematical reasoning and problem-solving approaches.

Discussion Character

  • Mathematical reasoning
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant suggests that if they work equally, the combined rate can be expressed as $$\frac{1}{12}+\frac{1}{12}=\frac{1}{6}$$ but struggles to align this with the problem's specifics.
  • Another participant proposes an equation based on the rates of Clarissa and Shawna, stating $$\frac{1}{c+5}+\frac{1}{c}=\frac{1}{6}$$ where $c$ represents Clarissa's time to complete the job alone.
  • A further contribution introduces a general approach, defining the rates of painting in terms of days per house and setting up an equation based on the total time taken together.
  • One participant derives a quadratic equation $$c^2-7c-30=0$$ through the least common denominator (LCD) method and factors it to find that $C=10$ days, while noting that other solutions found online were less clear or incorrect.

Areas of Agreement / Disagreement

Participants generally agree on the approach to solving the problem and arrive at the same conclusion regarding Clarissa's time to complete the job alone. However, there is mention of other solutions that differ, indicating some disagreement on methods or interpretations.

Contextual Notes

There are unresolved aspects regarding the derivation of equations and the assumptions made about the rates of work. Some participants express uncertainty about how to manipulate the equations to align with the problem's conditions.

Who May Find This Useful

This discussion may be useful for students or individuals interested in mathematical problem-solving, particularly in the context of work-rate problems and quadratic equations.

karush
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Clarissa and Shawna, working together, can paint the exterior of a house in $$6$$ days. Clarissa by herself can complete this job in $$5$$ days less than Shawna. How long will it take Clarissa to complete the job by herself?

well if they work equally then

$\frac{1}{12}+\frac{1}{12}=\frac{1}{6}$

but I didn't know how to change this to match what the problem says.

The answer is "Clarissa 10 days by herself".
 
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how about this if $c =$ Clarissa then

$$\frac{1}{c+5}+\frac{1}{c}=\frac{1}{6}$$
 
For this problem, we'll start more generally:

Given that it takes them 6 days to paint the house, we can let $c$ and $s$ be the rate of painting in days/house. Then, one way of setting an equation (such that the units cancel) and works with the question:

$$6 \text{ days }\cdot\left( \frac{1}{c \frac{\text{days}}{\text{house}}}+\frac{1}{s \frac{\text{days}}{\text{house}}}\right) = 1 \text{ house}$$

From the second part of the question, we can formulate another equation. What is it?
karush said:
how about this if $c =$ Clarissa then

$$\frac{1}{c+5}+\frac{1}{c}=\frac{1}{6}$$

That is correct because we know that $c=s-5$, then $s=c+5$ and we can plug that back into the first equation. How can we solve for $c$? (Wondering)
 
Last edited:
ok from this I got by LCD $$c^2-7c-30=0$$ factoring
$$\left(c+3\right)\left(c-10\right)=0$$
so $C$ has to positive $C=10$ days I saw some other solutions to this on the internet but MHB is really the best place to be. some solutions elsewhere really got messy with wrong answers
 

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