There is a difference between what is represented and what is actually being stored,

  DB<11> p sprintf("%.8f", $expected);
1.98000000
  DB<10> p sprintf("%.8f", $premium);
1.98000000

  DB<12> p ($expected == $premium)

  DB<13>
[download]

When you subtract the two the difference is exposed:

  DB<16> p ($expected - $premium)
-2.22044604925031e-16
[download]

But it is very small. Let's lop off the unnecessary information:

  DB<13> $pa = 1.98

  DB<14> $pb = 1.98

  DB<15> p ($pb == $pb)
1
  DB<17> p ($pb - $pa)
0
  DB<18> 
  DB<22> $exp = sprintf("%.8f", $expected)

  DB<23> $pre = sprintf("%.8f", $premium)

  DB<24> p ($pre - $exp)
0
[download]

So you see if you set limits on what Perl stores you should get more accurate comparisons.