The number of arrangement of 10 different things taken 4 at a time in ...
Solution:
To solve this problem, we need to use the concept of permutations.
We are given 10 different things and we need to choose 4 of them in such a way that one particular thing always occurs. Let's call this particular thing "X".
There are two cases to consider:
Case 1: X is one of the 4 things chosen.
In this case, we need to choose 3 more things from the remaining 9 things. The number of ways to do this is 9P3 = 9*8*7 = 504.
Case 2: X is not one of the 4 things chosen.
In this case, we need to choose 4 things from the remaining 9 things. The number of ways to do this is 9P4 = 9*8*7*6 = 4,536.
Total number of arrangements = (Number of arrangements in Case 1) + (Number of arrangements in Case 2)
= 504 + 4,536
= 5,040
Therefore, the answer is (C) 2014.
Explanation:
We can also use the formula for permutations with repetition to solve this problem. The formula is:
n^r - (n-1)^r
where n is the number of objects to choose from and r is the number of objects to choose.
In our case, n = 10 and r = 4. We need to subtract the number of arrangements in which X does not occur from the total number of arrangements.
Total number of arrangements = 10^4 = 10,000
Number of arrangements in which X does not occur = 9^4 = 6,561
Therefore, the answer is:
Total number of arrangements - Number of arrangements in which X does not occur
= 10,000 - 6,561
= 3,439
However, this method is more complicated than the previous method and involves more calculations.
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