Why are we using 29 as years and not 30? and if there was a situation where we used 30 instead of 29 how would that question be worded?

Much appreciated if someone could explain this to me!

on 12 12. Charlie Stone wants to retire in 80 years and he wants to have an annuity of $1,000 a year for 20 years after retirement. Charme wants to receive the first annuity payment at the end of the 30th year, using an interest rate of 10%, how much must Charlie invest today in order to have his retirement annuity (round to the nearest $10)? A. $490 B. $540 C. $570 D. $500 N = 20, l/Y = 10, PV = ?, PMT = 1000, FV = 0 PV -8,514 N-29,/Y-10, PV-?, PMT 0,FV-8514 53 1:29:54/2:24:5