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
