Question

how many 4 digit no. can be formed using0,1,2,3,4,5

Answer 1

There will be two cases in this question

• When repetition of digits is not allowed
• In this case, for the no. to be a 4-digit, first digit should not be 0. So, there are 4 possibilities. Next for the second digit can have any of the one other than the one used in the first place. So, again 4 possibilities. Similarly the third digit will have 3 possibilities (removing the two used digits) and the fourth has 2.so total no of 4-digit no. = 4*4*3*2=96

• When repetition of digits are allowed
• In this case the first digit can have any of the 4 (other than 0) and then remaining three places can take any value, so each has 5 possibilitiesso total no of 4-digit no. = 4*5*5*5 =500