# Let A be the set of 4-digit numbers a1 a2 a3 a4 where a1> a2> a3> a4, then n(A) is equal to

Q: Let A be the set of 4-digit numbers a1 a2 a3 a4 where a1> a2> a3> a4, then n(A) is equal to

(A) 126

(B) 10C4

(C) 210

(D) none of these

Sol. Any selection of four digits from the ten digits 0, 1, 2, 3, . . . , 9 gives one such number.

So, the required number of numbers = 10C4 = 210 .

Hence (B), (C) are the correct answer.