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Home Q & A Board Science-Related Homework Help Mathematics
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savio savio
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9 years ago Edited: 9 years ago, savio
Working together, Jack and Jill can complete an Electric Circuits assignment in 4 hours. It would take Jack 2 hours longer than Jill to complete the assignment alone. How long would it take Jill alone?

Could someone please show me how to solve this problem algebraically in detail with explanatio? It is a linear systems problem, but I can't seem to figure it out.
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Biology - The only science where multiplication and division mean the same thing.

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#1
9 years ago Edited: 9 years ago, metal_zelda
Let a=Jack's time and b=Jill's time. However, we are interested in rate, which is inversely proportional to time. Thus, 1/a+1/b=1/4, where 1/a is Jack's rate and 1/b is Jill's rate, where the units of rate are inverse hours.

We need to express a in terms of b or b in terms of a. According to the problem, Jill works two hours faster than Jack, so a=b+2 or b=a-2

From there, we can solve the system by substitution.

This problem appears to produce two non integer solutions, one of which is erroneous.
savio Author
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#2
9 years ago
I know the solution to this problem, but I never knew why it was 1 over a, and 1 over b, and 1 over 4. That's what was throwing me off, confusing me big time.

Thanks for the response.
Biology - The only science where multiplication and division mean the same thing.
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