Probability ice cream flavor problem

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The problem involves determining the number of combinations for three scoops of ice cream from four flavors: chocolate, cookies, strawberry, and vanilla, allowing for repetitions. The confusion arises from interpreting the question's wording, particularly regarding combinations versus permutations. The correct approach includes three scenarios: all scoops the same flavor, all scoops different flavors, and two scoops of one flavor with one scoop of another. The total combinations, accounting for these scenarios, correctly sum to 20. Understanding the distinction between combinations and permutations is key to solving this problem accurately.
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Homework Statement


There are four ice cream flavors; chocolate,cookies,strawberry and vanilla.

How many different combination of flavors of three scoops of ice cream are possible if it is permissible to make all three scoops the same flavor?



Homework Equations





The Attempt at a Solution



The answer is 20.

But i am very confused about the wording of the question.
If only all three scoops with same flavor is counted as a different combination, shouldn't it be just 4(three scoops of same four flavors) + 4*3*2 ( all different flavors combination)

then it gives me 28 which is wrong..

What's the point of this question and how to approach to it?

Could someone help me out here?
 
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4*4*4 = 64 possibilities
 
The 4*3*2 you calculated is the number of permutations, but the question asks for the number of combinations.

The question is a bit unclear, but I think I understand what they want. The possibilities you have for constructing flavor combinations are: 3 scoops all different flavors, 3 scoops all the same flavor, and 2 scoops of one flavor and 1 scoop of a second flavor. They seem to be counting, for example, two scoops of strawberry and one scoop of vanilla as a different flavor combination from two scoops of vanilla and one scoop of strawberry. If you add all those up, it comes out to 20.
 
I tried to combine those 2 formulas but it didn't work. I tried using another case where there are 2 red balls and 2 blue balls only so when combining the formula I got ##\frac{(4-1)!}{2!2!}=\frac{3}{2}## which does not make sense. Is there any formula to calculate cyclic permutation of identical objects or I have to do it by listing all the possibilities? Thanks
Since ##px^9+q## is the factor, then ##x^9=\frac{-q}{p}## will be one of the roots. Let ##f(x)=27x^{18}+bx^9+70##, then: $$27\left(\frac{-q}{p}\right)^2+b\left(\frac{-q}{p}\right)+70=0$$ $$b=27 \frac{q}{p}+70 \frac{p}{q}$$ $$b=\frac{27q^2+70p^2}{pq}$$ From this expression, it looks like there is no greatest value of ##b## because increasing the value of ##p## and ##q## will also increase the value of ##b##. How to find the greatest value of ##b##? Thanks
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