Question 1026874
You want to change the equation from viewing as a yearly period to view as a monthly period. 


{{{1-11/12}}} will give the rate kept for a one-month period.


Next is to make the adjustment for amount of time.  t is still YEARS.  You know the fact  12 months IS 1 year.
{{{t*years*12(months/year)=12t*months}}}, so you seem to ALMOST have the formula correct -----just need the proper grouping symbols for the rendering into "notation".


{{{P=V(1-r/12)^(12t)}}}-------------but remember --- t is used in YEARS.