Correct Answer - Option 1 : 504
Concept:
Permutation: Permutation is defined as an arrangement of r things that can be done out of total n things. This is denoted by
\({\;^n}{P_r} = \frac{{n!}}{{\left( {n - r} \right)!}}\)
Calculation:
Here order matters for example 123 and 132 are two different numbers. Therefore, there will be as many 3 digit numbers as there are permutations
of 9 different digits taken 3 at a time.
Therefore, the required 3 digit numbers
⇒ In 3rd place required number = 9
⇒ in 2nd place required number = 8
⇒ In 1st place required number = 7
So, 3 - digit number form by
⇒ 9 × 8 × 7
⇒ 504
Combination: The number of selections of r objects from the given n objects is denoted by
nCr = \(\rm \frac{n!}{r! (n - r)!}\)
