Permutation and CombinationHard
Question
An n digit number is a positive number with exactly n digits. Nine hundred n- digit numbers are to be formed using only the three digits 2, 5 and 7. The smallest value of n for ehich this is possible, is
Options
A.6
B.7
C.8
D.9
Solution
Distinct n digit numbers which can be formed using digits 2, 5 and 7 are 3n We have to find n so that
3 n ≥ 900 ⇒ 3n-2 ≥ 100
⇒ n - 2 ≥ 5
⇒ n ≥ 7 so the least value of n is 7.
3 n ≥ 900 ⇒ 3n-2 ≥ 100
⇒ n - 2 ≥ 5
⇒ n ≥ 7 so the least value of n is 7.
Create a free account to view solution
View Solution FreeMore Permutation and Combination Questions
If all the letters of the word ″QUEUE″ are arranged in all possible manner as they are in a dictionary, then...Eight chairs are numbered 1 to 8. Two women and three men wish to occupy one chair each. First, the women choose chairs ...Find the total number of ways of answering 5 objective type questions, each question having 4 choices....nPn is equal to-...How many signals can be given by means of 10 different flags when at a time 4 flags are used, one above the other?...