Numbers
To reuse a similar calculation in multiple locations in your spreadsheet, you can copy and paste functions and formulas from one cell to other cells.
When the keyboard is closed, you can copy a formula, or just the result, from one cell to another.
Go to the Numbers app on your iPad.
In a spreadsheet, tap the cell with the formula you want to copy, tap it again, then tap Copy in the contextual menu.
Tap the cell where you want to paste the formula or the result, tap it again, then tap Paste.
To preserve the formula, tap Paste Formulas, or to paste only the result, tap Paste Values.
Go to the Numbers app on your iPad.
In a spreadsheet, double-tap the cell with the formula you want to copy.
Tap to the right of the formula in the Formula Editor above the keyboard, then tap Select.
Drag the blue selection handles to encompass only the part of the formula you want to copy, then tap Copy.
Tap .
Tap the cell where you want to paste the partial formula, then tap above the keyboard on the right.
Tap in the Formula Editor where you want to insert the partial formula, tap Paste, then tap .