Selecting items from list and attaching ratios to selection
 

I am struggling with the following.

I would like to set up a sheet whereby I send the following to a user which
would be in cells A1 and B1.

Fund A $1m

The user would then return the spreadsheet with the following

Fund A $1m GBP,EUR,USD 0.5,0.4,0.1

having updated cells 3 currencies in cell C1, and 3 ratios (equalling 1) in
cells D1. This corresponds to fund A being made up of $500k in GBP, $40Ok in
EUR, and $100k in USD.

I would like to create a form, probably activated on selection of the
currency cell (column C), listing all currencies from an agreed list of 80
currencies. (That bit I can do). And to select a small number of those
currencies, and then input the correpsonding ratios for those selected
currencies, whilst ensuring that the ratios for each fund total 1.

The bit I am struggling with is inputing the ratios and keeping them
associated to the relevant currency. Because as illustrated above, I then
need to use the ratios for calculation, or at least have array records of
them that I can use for calculaton purposes.

I need to do this as I have a large list of funds.

Any help, greatly appreciated.
--
Thanks,
Adrian.