There are 50C3 = 50!/(3!47!) = 19,600 such possible combinations. The list [could] start:
{1, 2, 3}, {1, 2, 4}, {1, 2, 5}, {1, 2, 6}, ...
and end:
..., {47, 48, 49}, {47, 48, 50}, {47, 49, 50}, {48, 49, 50}.
I'll let you fill in the other 19,592 combinations.
There are 840 4-digit combinations without repeating any digit in the combinations.
There are 35C4 = 35*34*33*32/(4*3*2*1) = 52,360 combinations.
11
There are only five combinations: 1234, 1235, 1245, 1345 and 2345.
The number of combinations, denoted by 11C6 is 11!/[6!*(11-6)!] = 11*10*9*8*7/(5*4*3*2*1) = 462
6
Without repeating, 4. With repeating, 8.
We won't be able to answer that without knowing the numbers.
There are 46C5 = 46*45*44*43*42/(5/4/3/2/1) = 1,370,754 of them and I am not stupid enough to try and list them. You are welcome to try, though.
1,023,456,789
5040
From 1 to 20, you can pull out 15,504 different groups of 5 numbers, and each group can be lined up in 120 different orders.