Question Details

If n(X) = mC6, then the value of m is ______.

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Correct Answer :

20

Solution :

The correct answer is 20.

To find the value of m in the given equation, we need to analyze the underlying mathematical context of this problem, which is typically defined as follows:

Let S={1,2,3,4,5,6} be a set. Let X be the set of all relations R from S to S such that:
1. R has exactly 6 elements (ordered pairs).
2. For each ordered pair (a,b)R, the condition |a-b|2 is satisfied.

We want to find n(X), which is the total number of such relations.

Step 1: Determine the total number of ordered pairs in S×S
The number of elements in set S is 6. Thus, the total number of ordered pairs in the Cartesian product S×S is:
6×6=36

Step 2: Count the ordered pairs (a,b) that do NOT satisfy the condition |a-b|2
The pairs that do not satisfy the condition are those where:
|a-b|<2
This means either |a-b|=0 or |a-b|=1.

Case 2.1: |a-b|=0 (i.e., a=b)
These are the diagonal elements. There are 6 such pairs:
(1,1),(2,2),(3,3),(4,4),(5,5),(6,6)
Total = 6 pairs.

Case 2.2: |a-b|=1
These are the pairs of consecutive elements: - If a<b, the pairs are: (1,2),(2,3),(3,4),(4,5),(5,6) (5 pairs)
- If a>b, the pairs are: (2,1),(3,2),(4,3),(5,4),(6,5) (5 pairs)
Total = 5+5=10 pairs.

Summing the excluded pairs:
6+10=16 pairs

Step 3: Calculate the number of allowed pairs
Subtracting the excluded pairs from the total pairs:
36-16=20 allowed pairs

Step 4: Find the number of relations in X
A relation R in X is formed by choosing exactly 6 ordered pairs from the 20 allowed pairs. Therefore, the number of such relations is given by the combination formula:
n(X)=C620

Step 5: Determine m
Comparing the expression to the given equation n(X)=C6m, we have:
C6m=C620
This directly gives:
m=20

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