General :: Delete Rows Based On Values In A Column Using Sed?

I have a lot of files with thousands of rows and usually two columns of data. Column 1 is a coordinate, column 2 is a score. I want to delete rows that have a value in column 2 over, in this case, 50.

For example, here's a clip from a file:

2999898 39
2999899 40.9
2999900 42.7
2999901 44.7
2999902 46.7
2999903 48.9
2999904 51.1
2999905 53.3
2999906 55.7

I want the output to be this:

2999904 51.1
2999905 53.3
2999906 55.7

I know how to use sed for very basic things like deleting rows or ranges of rows but I can't figure out this ostensibly easy command.