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Re: Working at their respective constant rates, Machine A takes 2 days [#permalink]
grenico wrote:
Answer is A.

The time it takes Machine A to make \(w\) widgets is 6 days, so to make \(2w\) widgets it would take 12 days.

I used algebra to solve this one and it's a pain to do, but will write it out if someone needs help with explanation :)

Can you please explain this?
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Re: Working at their respective constant rates, Machine A takes 2 days [#permalink]
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Shortcut:

Work done by A + Work done by B = Total Work done
i.e. \(W_A + W_B = W_T\) ........ (1)

We know, Work = (Rate)(Time)

Let, Time required by machine B to produce \(w\) widgets be \(t\)
Then, Time required by machine B to produce \(w\) widgets will be \((t+2)\)

\(R_A = \frac{1}{(t+2)}\)
\(R_B = \frac{1}{t}\)

Total work done is \(\frac{5}{4}\) in 3 days
Now, using equation (1);

\(\frac{3}{(t+2)} + \frac{3}{t} = \frac{5}{4}\)

\(12t + 12t + 24 = 5t^2 + 10t\)
\(5t^2 - 14t - 24 = 0\)

Solve for \(t = 4\)
i.e. Machine will take \(4 + 2 = 6\) hours to produce \(w\) widgets

Col. A: \(6 + 6 = 12\)
Col. B: \(10\)

Hence, option A
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Re: Working at their respective constant rates, Machine A takes 2 days [#permalink]
Hi there, is there a way to get to the solution faster ? I managed to get to the right solution by finding t = 4 but it took me like 4 minutes so no way I can afford that :)
Thank you in advance guys
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Re: Working at their respective constant rates, Machine A takes 2 days [#permalink]
Expert Reply
The solution provided above by Karun would take roughly 40 seconds.

I do not think is a big deal
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Re: Working at their respective constant rates, Machine A takes 2 days [#permalink]
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