JEE Main2018MathematicsPermutation and CombinationActual
n -digit numbers are formed using only three digits 2 , 5 and 7 . The smallest value of n for which 900 such distinct numbers can be formed is :
Options
- A9
- B7
- C8
- D6
Correct answer
B. 7
Step-by-step solution
n - digit number are formed using only three digits 2 ,   5 and 7 with repetition = 3 n . Since, 3 6 < 900 and 3 7 > 900 So, n = 7 .