In a certain computer company, 3/5 of the programmers know fortran, 1/6 know cobol, and 1/10 know both. what fraction know neither fortran nor cobol?

Given that 3/5 know fortran

1/6 know cobol

1/10 know both fotran and cobol

the fraction of programmers who knows at least one of the two programs will be:

3/5+1/6+1/10

=13/15

the fraction of programmers who don't know either of the two will be:

1-13/15

=2/15

thus the answer is 2/15