A customer remembers that 2, 4, 7, and
9 are the digits of a four-digit access code for an automatic
bank-teller machine. Unfortunately, the customer has forgotten
the order of the digits. Find the largest possible number
of trials necessary to obtain the correct code.
38 ATM access code Work Exercise 37 if the digits are

Question

A customer remembers that 2, 4, 7, and
9 are the digits of a four-digit access code for an automatic
bank-teller machine. Unfortunately, the customer has forgotten
the order of the digits. Find the largest possible number
of trials necessary to obtain the correct code.
38 ATM access code Work Exercise 37 if the digits are

rock_mit182 · Answer

ATM access code Work Exercise 37 if the digits are 2, 4,
and 7 and one of these digits is repeated in the four-digit
code.

rock_mit182 · Answer

for the first one would it be 4 ! ?

anonymous · Answer

Yes.

rock_mit182 · Answer

what about the second one ?

rock_mit182 · Answer

3 ! ?

rock_mit182 · Answer

I need to understand how to solve it

rock_mit182 · Answer

Numerical palindromes A palindrome is an integer, such
as 45654, that reads the same backward and forward.
(a) How many five-digit palindromes are there?
(b) How many n-digit palindromes are there?