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Re: A retail business has determined that its net income, in ter [#permalink]
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The quadratic method is indeed correct. There is a riskier plugging method.

Rewrite the equation: \(x^2+x-380=0\) as \(x^2+x=380\)

\(x(x+1)=380\).

So 380 is product of 2 consequtive integers x and x+1. Factorizing 380 we get 19, 5, 2, 2. So we can rewrite 380 as 19*20 (two consecutive integers).

Hence x=19.

PS: in real exam this method might be risky and might consume too much time to implement.
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Re: A retail business has determined that its net income, in ter [#permalink]
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mohan514 wrote:
PIneappleBoy2 wrote:
I solved the problem using the quadratic formula, but I welcome other ways on how to do it faster.

a=1, b=1, c= -380

x= \(\frac{-1+-\sqrt{1^2-4(1)(-380)}}{2(1)}\)

x= \(\frac{-1+-\sqrt{1521}}{2}\)

x= \(\frac{-1+39}{2(1)}\) and x= \(\frac{-1-39}{2}\)

X= \(\frac{38}{2}\) and x= \(\frac{-40}{2}\)

x=14 and x=-20.

Since we are looking for a positive integer, we can disregard -20 and only look at x=14.

Quantity A = 14
Quantity B = 10

Quantity A is greater.

The answer is A.


38/2 is 19 BTW.

How do we know square root of 1521 is 39?

I think we can just consider about the symobl the number would have and conclude as positive vs negative. Correct me if I am wrong.

Also is that the only way to solve this problem?


Just edited my original post to reflect that the answer is actually 19, not 14. Thank you for that.

We are able to find that 39 is the square root of 1521 through the use of the GRE Calculator.

As for concluding the positive vs. negative, you are correct. I just wrote it out since it was a part of the quadratic equation.
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Re: A retail business has determined that its net income, in ter [#permalink]
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Here, x (Square)+x−380 = 0
Then, x (x+1) = 380
Then, x (x+1) = 19 * 20
Then, x (x+1) = 19 * (19+1)
So, x = 19
Ans: A
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Re: A retail business has determined that its net income, in ter [#permalink]
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Column A: If the net income = 0, then x² + x - 380 = 0
Let's solve this equation by factoring: (x + 20)(x - 19) = 0
So, x = -20 or x = 19
Since x (the number of items sold) cannot be NEGATIVE, we can be certain that x = 19
So, Column A = 19
Column B = 10

Correct answer:
Show: ::
A


Cheers,
Brent
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Re: A retail business has determined that its net income, in ter [#permalink]
First of all, we had to know that items can NOT be negative.

Then, for the net income \(x^{2}\) + x - 380 to be 0. We can do the factorization (x+20)(x-19). We get x=19 or -20.

since items can not be negative. Quant A is 20 which is bigger than Quant B (10).
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Re: A retail business has determined that its net income, in ter [#permalink]
Thank you
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Re: A retail business has determined that its net income, in ter [#permalink]
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put x = 10 (10 is taken from RHS)
then it shows that LHS= 10^2+10-380= -270
"-ve" sign shows that "x" should be increases to make the difference zero.
therefore LHS>10.
Note: if we go below the value of 10, suppose x=9, LHS becomes 9^2+9-380= -290, difference is increasing. and x can not be negative as x=-10 means negative product sold which is not real.
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Re: A retail business has determined that its net income, in ter [#permalink]
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