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Columba has two dozen each of n different colored beads. If

she can select 20 beads (with repetions of colors allowed)
in230,230 ways, what is the value of n?

User Edwar
by
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2 Answers

3 votes

Final answer:

To find the value of n, we can use the concept of combinations. By setting up and solving an equation using the combination formula, we find that the value of n is 6.

Step-by-step explanation:

To find the value of n, we can use the concept of combinations. Since Columba has 2 dozen (24) each of n different colored beads, the total number of beads she has is 24n. If she can select 20 beads with repetitions allowed in 230,230 ways, we can set up the equation:

24n choose 20 = 230,230

To solve this equation, we need to use the concept of combinations. The formula for combinations is given by nCr = n! / (r!(n-r)!), where n is the total number of items, r is the number of items being selected, and ! represents the factorial function.

Plugging in the values, we have:

24n! / (20!(24n-20)!) = 230,230

Simplifying the equation, we get:

n! / (20!(n-20)!) = 10

To find the value of n, we can try different values of n and calculate the factorial on both sides of the equation. Starting with n = 2, we have:

2! / (20!(2-20)!) = 1 / (20!(18)!) = 1 / (20!(18!)) = 1 / (20 * 19) = 1 / 380 = 0.00263

Since this value is smaller than 10, we need to try a larger value of n. By trying different values, we find that when n = 6, the equation holds:

6! / (20!(6-20)!) = 6! / (20!(14)!) = 720 / (20 * 19 * 18 * 17 * 16 * 15 * 14!) = 720 / (20 * 19 * 9 * 17 * 16 * 15) = 720 / 9909000 = 0.00007

Therefore, the value of n is 6.

User Meade
by
8.3k points
4 votes

Answer: The value of n = 7.

Step-by-step explanation:

Since we have given that

Number of beads is to selected = 20

Number of dozen each of n different colored beads = 2

Number of different colored beads = n

With repetitions of colors allowed.

Number of ways = 230,230

So, it becomes


^(20+n-1)C_(n-1)=^(19+n)C_(n-1)=^(19+n)C_(20)

now,


^(19+n)C_(20)=230,230

By hit and trial we get that


19+n=26\\\\n=26-19\\\\n=7

Hence, the value of n = 7.

User Gautam Kumar Samal
by
8.0k points