[Tutor] Looking for duplicates within a list

[Ken G.]

I have been working on this problem for several days and I am not making 
any progress.  I have a group of 18 number, in ascending order, within a 
list.  They ranged from 1 to 39.  Some numbers are duplicated as much as 
three times or as few as none.

I started with one list containing the numbers.  For example, they are 
listed as like below:

a = [1, 2, 3, 3, 4]

I started off with using a loop:

    for j in range (0, 5):
    x = a[0] # for example, 1

How would I compare '1' with 2, 3, 3, 4? 

Do I need another duplicated list such as b = a and compare a[0] with 
either b[0], b[1], b[2], b[3], b[4]?

Or do I compare a[0] with a[1], a[2], a[3], a[4]?

In any event, if a number is listed more than once, I would like to know 
how many times, such as 2 or 3 times.  For example, '3' is listed twice 
within a list.

TIA,

Ken