Question
Download Solution PDFIf n - 1P3 ∶ n + 1P3 = 5 ∶ 12, then n is
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFFormula used:
Calculation:
Given that
n - 1P3 ∶ n + 1P3 = 5 ∶ 12
We know that,
⇒
⇒
⇒
⇒ 12n2 - 60n + 72 = 5n2 + 5n
⇒ 7n2 - 65n + 72 = 0
⇒ 7n2 - 56n - 9n + 72 = 0
⇒ (n - 8)(7n - 9) = 0
⇒ n = 8
Additional Information
Number of Permutations:
A number of all permutations of n things, taken r at a time, is given by:
nPr = n!/(n - r)!
Combinations:
Each of the different groups or selections which can be formed by taking some or all of a number of objects is called a combination.
Number of Combinations:
The number of all combinations of n things, taken r at a time is:
nCr = n! /(r!) (n - r)!
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