Let $A$ be the set of 4 digit number ${a_1}{a_2}{a_3}{a_4},\;{\rm{where}}\;{a_1} < {a_2} < {a_3} < {a_4},$ then $n\left( A \right)$ is equal to

JEE MATHEMATICS MCQ: COMBINATIONS

1 Easy

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Application +4 | -1

Let

A

be the set of 4 digit number

{a_1}{a_2}{a_3}{a_4},\;\mathrm{where}\;{a_1} < {a_2} < {a_3} < {a_4},

then

n\left( A \right)

is equal to

View answer and explanation

Correct option: B

126

Option B (126) is correct because it calculates the number of ways to choose 4 distinct digits from the set {1, 2, 3, 4, 5, 6, 7, 8, 9} where the order is strictly increasing.

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