use warnings;
use strict;
use Math::BigFloat;
use feature ':5.10';

my $x = Math::BigFloat->new('954846259588805228035541587771');

print $x * 2, "\n";
print $x * 2.5, "\n";
print $x * Math::BigFloat->new('2.5'), "\n";
print $x * "2.5";

__END__

Outputs:

1909692519177610456071083175542
2387115648972013070088853969427.5
2387115648972013070088853969427.5
2387115648972013070088853969427.5