Apple Numbers: how to change a date format to a number format In Apple Numbers the app can work out the number of days between dates, but then if I times this by a number (ie, a %interest rate and an amount of money) Numbers insists that the answer is a number of days!  Even if I go to Cell>Date Format and change it.  The system ignores this and returns to displaying the answer as a number of days.  How do I force the system to show this cell as a number and not in the date / days format?
You can use a function to convert the duration to a plain number.  For example, if difference between the dates in in E4, and it's 10 days, then...

=DUR2HOURS(E4) × 0.1


Shows a number, 24.0. There are other functions that you might use: DUR2DAYS, etc.