I suspect that the issue here is the number of parenthesis that you included. Try encompassing the <= and >= comparisons with parenthesis themselves and see if that makes a difference. By <= and >= comparisons, I mean rewrite (a <= 800 && a >= 200) to ((a <= 800) && (a >= 200))
Still says it's valid even though it shouldn't be.
1 2 3 4 5 6 7 8
Enter 1000 for the first value to end this program
Enter First Score: -30
Enter Second Score: 40
Enter Third Score: 50
-30 is invalid
40 is invalid
50 is invalid
this group is valid