Andre wrote:
1. Say you decided to invest 24 280 for 10 years and say on maturity it is
worth 68 941 - How do I calculate that in Excel with an Excel
function/formula?

How do you calculate what: the rate of return? If so:

=rate(10, 0, -24280, 68941)

2. If I said that the maturity value (68 941) is 29 121 in today's money -
How would I calculate that in Excel with an Excel function/formula?

Over how many years: 10 again? If so:

=rate(10, 0, -29121, 68941)

3. Lastly if I said that the final amount (29 121) would give me a monthly
pension of 291 per month. How would I calculate that in Excel with an Excel
function/formula?

Do you really mean "final amount"? 29121 was the initial amount in #2.
And over how many years: 10 again?

To compute the __monthly__ rate of return if you invested 29121 and you
wanted 291 per month and 68941 after 10 years:

=rate(10*12, 291, -29121, 68941)

The compounded annual rate of return can be computed with either one of
the following:

=fv(rate(...), 12, 0, -1) - 1

=(1 + rate(...))^12 - 1