How many numbers, each of 4 digits, can be formed from the digits 3, 4, 5, 6 when each digit can be repeated 4 times? Calculate the sum of all the numbers.

There are 4 choices for each digit, and since each digit can be repeated 4 times, there are a total of 4^4 = 256 possible numbers.

To calculate the sum of all the numbers, we first find the sum of all the digits: 3 + 4 + 5 + 6 = 18.

Since each digit appears 4 times in each number, the sum of each number is 18 * 1111 = 19998.

Therefore, the sum of all 256 numbers is 256 * 19998 = 511968.

Total number of 4-digit numbers that can be formed = 4 - 4 - 4 - 4 = 256

Sum of the numbers = (3 + 4 + 5 + 6) - 256 - 1111
= 18 - 256 - 1111
= 458688

Therefore, the sum of all the numbers is 458688.