usage of the last list number value so that it can be used inside of a formula in writer

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What you need is a cross-reference. It works both with dedicated paragraph styles associated with a list style and with paragraphs numbered with the toolbar button.

(in a sophisticated document aiming at professional quality, I'd recommend avoiding the toolbar button to create numbered lists.)

Where you want to insert the number of a question (the number of the list item), Insert>Cross-reference, Cross-references tab. In the Type box, select Numbered Paragraphs, in the Insert reference to, Number. In the Selection list, click on the numbered paragraph you're interested in. Push Insert.

Pay special attention to "the number of a question". Please note I didn't write "the current value of the numbering counter" or "the final value of the counter". You create a reference to a specific question. If you add other items before the question, the cross-reference will be automatically updated, but if items are added after the question, the question number is not modified.

This means you must manually make sure the cross-reference points to the last question.

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