#!/usr/bin/perl

@times = (23.0, 22.7, 24.5, 20.0, 25.2, 19.8, 22.4, 24.0, 23.1, 23.3,  24.1, 26.9);

sub mean {
    my ($arrayref) = @_;
    my $result;
    foreach (@$arrayref) { $result += $_ }
    return $result / @$arrayref;
}

sub z_significance_one_sided {
    my ($arrayref, $expected_mean, $expected_variance) = @_;
    return (mean($arrayref) - $expected_mean) /
        sqrt($expected_variance / @$arrayref);
}

if (($z = z_significance_one_sided(\@times, 24, 1.5)) <= -1.64) {
    print "z is $z, so the difference is statistically significant. \n";
} else {
    print "z is $z, so the difference is not statistically significant. \n";
}