If I understand your interest correctly, I think Simulate ( https://www.jmp.com/support/help/en/17.1/#page/jmp/simulate.shtml# ) is what you need.

The idea is so sub-sample from your data and fit Lognormal repeatedly and collect summary statistics. I attach a modified Big Class sample data to illustrate.

Run the script in the data table. It fits Lognormal to "weight" variable, but use "random freq" as Freq.

Now right click on a statistic of interest, and choose "Simulate":

In the dialog, choose "random freq" on both sides, click Ok:

And you will get a table like the following:

The last two columns are the summary statistics of individual fits to sub-samples.

The "random freq" column use "Resample Freq" function:

What you need to do is to tweak the threshold in the column formula, so you can get the total of 5/10/20 as you wish.