Question

Rani had a savings accound in the bank.the password of her atm card was a four digit number.after a month of teceiving her password she forgot it.she only remembered that all its digits were distinct.no password issued by bank starts with 0.find the maximum number of trials she had to enter the correct password

Answer 1

Let's consider four blanks _ _ _ _
The first digit is 0
The next 3 blanks can be filled with any number from 1-9 provided no number repeats in 9p3 ways which is equal to 9*8*7=504 ways