Problem with entering formulas in data validation cells

I have two Excel problems, which are similar, so I've included them both in one post. I hope someone can help.

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Problem 1

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I have two sheets - Sheet A and Sheet B. In each sheet, there is a cell where a frequency can be entered (weekly, 2-weekly etc), and each cell contains a dropdown which refers to a list. When a frequency is chosen on Sheet A, I want the same frequency to auto-populate in Sheet B. So I tried using this formula in the cell in Sheet B:

=IF(SHEET A!C4="","",SHEET A!C4)

...or I suppose I could just use:

=(SHEET A!C4)

Anyway, it wouldn't let me enter the formula, because of the data validation only allowing "weekly", "2-weekly" etc.

So I tried creating the formula in another cell and referring to that cell instead:

=IF(SHEET A!C4="",C4="",C4=SHEET A!C4)

But using this formula doesn't auto-populate Sheet B C4 for me, it just returns "TRUE" or "FALSE" in the cell where this formula is entered.

Is there any way I can get this to work, without removing the Data Validation from the cell (which I need to keep in place)?

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Problem 2

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I have two cells which I want to be populated automatically in SHEET A, using figures from SHEET B. One is a currency amount, and the other is a frequency ("weekly", "2-weekly" etc). So I use these formulas:

=IF('SHEET B'!D22=0,"",TEXT('SHEET B'!D22,"£0.00")))
=IF('SHEET B'!D22=0,"","monthly"))

Formula #1 does work, but Formula #2 doesn't (I get the same problem as with Problem 1, where it won't let me enter the formula, because of the data validation). And it doesn't look great with only one formula working, because the cells are then only half-populated.

So I tried the same alternative method as I tried with Problem 1, placing the formulas in alternative cells:

=IF('SHEET B'!D22=0,B20="",B20=TEXT('SHEET B'!D22,"£0.00")))
=IF('SHEET B'!D22=0,C20="",C20="monthly"))

But again these just produce "TRUE" or "FALSE" in the formula cells, and nothing in the reference cells.

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So my problems seem to be:

1 - I can't enter formulas in data validated-cells, even if the results of the formula are within the parameters of the data validation list (i.e. nothing at all, or something from the list)
2 - I can't auto-populate a referenced cell by placing a formula in another cell somewhere else

If I had a choice, I would actually prefer to have the formulas in other cells, because sometimes figures will be entered directly into the other cells, so it would make things look better if there were no formulas in the "main" cells".

Unfortunately I can't upload the workbook because it's not mine. But I can explain the situation.

When someone enters a currency figure and selects a frequency on SHEET A (e.g. "£360" and "monthly"), the chances are that the frequency will need to be the same (in this case "monthly") on SHEET B. So I want the frequency cell on SHEET B to be automatically populated when a frequency is chosen on SHEET A. But I can't just make the frequency cell on SHEET B equal to the frequency on SHEET A, because there may be the odd occasion where the frequencies are different, and so I have to be able to allow the user to alter the frequency on SHEET B accordingly.

Well yeah, I do want the frequency to auto-populate, but I still need to give the user the opportunity to say "actually in this case, the frequencies are different", and then be able to modify the second frequency accordingly. That would be a very rare situation, but one I would have to allow for. But the vast majority of the time, the frequencies would be the same, which is why I wanted it to auto-populate. But it seems like it would be a lot of work to get that working.

If I could get it to work, then it would actually be auto-populating two cells, and when time is of the essence, that can help things. Especially because there will be another sheet, which if used, could auto-populate the figure, which would mean that up to four cells could be populated automatically. So I think it is worth the effort if I can get it to work.

Thanks for the link, I'll give that I look and see if I can get it to work.

If I could get it to work, then it would actually be auto-populating two cells, and when time is of the essence, that can help things. Especially because there will be another sheet, which if used, could auto-populate the figure, which would mean that up to four cells could be populated automatically. So I think it is worth the effort if I can get it to work.

Thanks for the link, I'll give that I look and see if I can get it to work.

Well one of the problems I'm working on is, a Gross Wage is entered on one sheet (amount in one cell, payment frequency in another), then the Tax and National Insurance amounts are entered on another sheet in the same way. I wanted to set it up so that as soon as a frequency is selected for the Gross Wage using a data validation pulldown, that same frequency is automatically completed for the Tax and NI on the other sheet.

Now as much as I can't ever see there being a situation where the Gross Wage frequency would differ from the Tax or NI frequency, I still have to allow the user to do that, which prevents me from just saying "tax and NI frequency equals gross wage frequency".

And if I get rid of the validation on the Tax and NI sheet, then it would work as long as the payment frequencies matched, but if they didn't, then the user would have to type the frequencies of the Tax and NI in manually, which wouldn't be ideal, because calculations are made based on the frequencies of various cells.

I just thought it might be easier than this to, say, make the Tax and NI have their pulldowns, and let the default value of each pulldown be whatever the Gross Wage frequency pulldown is, and then the user would still be free to change the Tax and NI frequencies should they need to.