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Bunuel
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Hi Bunuel,
could you please help here ?
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how did you factor out "n^4 +33*n^2 + 38n - 12*n^3 -168 = 0" in to
(n+2)(n^3 -14n^2 + 61n -84) = 0
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Is there any simple way to solve this ? solving a 4 degree equation seems hard and takes too long.
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How did we arrive at the factors of the polynomial
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vipulgoel
how did you factor out "n^4 +33*n^2 + 38n - 12*n^3 -168 = 0" in to
(n+2)(n^3 -14n^2 + 61n -84) = 0


Please see the following link.
https://www.youtube.com/watch?app=desktop&v=xY7Vpxvm62A

It will help you answer your question.

The detailed answer is given below :

Once you have figured out 2 using the method as per the above link, You can try out using the smallest factors of 84 like 2 and 3. You immediately get 3 as the root. Then you are left with a quadratic equation that is easy to solve, giving you 7 and 4 as the roots.

Then the sum of positive roots becomes 7+4+3 = 14.

Hope this helps.
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Nobody’s factoring 4th degree polynomials on the GMAT

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Given: There are five different coins of five different colors: red, blue, green, yellow, and white.

The value of 1 red coin = the value of n blue coins;
The value of 1 blue coin = the value of n green coins;
The value of 1 green coin = the value of n yellow coins;
The value of 1 yellow coin = the value of n white coins.

Asked: If the value of 12 blue coins and 168 white coins equals to the value of 1 red coin, 33 green coins, and 38 yellow coins. What is the sum of all possible values of n if n is a positive integer?

The value of 1 yellow coin = the value of n white coins
The value of 1 green coin = the value of n^2 white coins
The value of 1 blue coin = the value of n^3 white coins
The value of 1 red coin = the value of n^4 white coins

12n^3 + 168 = n^4 + 33n^2 + 38n
n^4 - 12n^3 + 33n^2 + 38n - 168 = 0
n = {-2,3,4,7}

Sum of all possible values of n when n is a positive integer = 3+4+7 = 14

IMO E
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Can someone please help me confirm if my thought process for solving is correct or not?

My Solution ->

Instead of focusing on getting the roots of polynomial. I wrote -168 (as it is the product of roots) as 2 * 2 * 2 * 3 * 7. By observation, I can see that if we take roots as (-2), (4), (3) and (7), the sum of roots condition is getting satisfied (i.e. -> -2+4+3+7 = 12).

Then to confirm this theory, I substituted -2 in the equation and got 0.

Hence, sum of positive integers = 14.

Is this though process correct or am I just overcomplicating things? Please do let me know if there is a better way of solving. Thanks!


Bunuel

Quote:
There are five different coins of five different colors: red, blue, green, yellow, and white.

The value of 1 red coin = the value of n blue coins;
The value of 1 blue coin = the value of n green coins;
The value of 1 green coin = the value of n yellow coins;
The value of 1 yellow coin = the value of n white coins.

If the value of 12 blue coins and 168 white coins equals to the value of 1 red coin, 33 green coins, and 38 yellow coins. What is the sum of all possible values of n if n is a positive integer?

A. 7
B. 10
C. 11
D. 12
E. 14



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