In the pra&icë of afîurances on the .furviv.br/hjp
of one life beyond ânother, there is fréquent occafion for making fuch afîurances, for a term of years only. The mëthod of determining the value in fuch cafes I have not.feen any where defcrïbed. Perhaps, therefore, a brief. account of it hère may be of fome ufe.
By reafoning in the famé manner with Mr. Simpfon,
p, 322, Seleél Exercifes, it will appear, that the value of any givcn fum S affured, for n years on a given life A, providcd in that time another given life B fliould furvive A, ;s x – 7- + – r~ + – r,.&c.(continued to n ternis) -U x -7- 4- -7-1 4- -,– ,&c. (con<? 2~r~~2/;r 2/1 rH
tinued likewife to n ternis) r denotïng 1 "increafed by its intereft for one year and a and l>, the numbers in the table of observations alive at the ages of A-. and B, 'diviùi-'d by the quotient arifing from dividing the ium of the différences in the table from thefe a
va!;ie requircd. But • 1 ̃] &c. is half the per- 2 t' 17' ` 2 Y
n – I n – I n – il1 – 2 1F^~ 1 'n – 2 Y
2n r 2n r 7.nlr -znr1 2m'1 in]r~
71-1 7t "l
-f 2'i r ̃ + 2H >' 2 n' – > s – Sic. is half the value of the joint z r, r 27t 7 2 j livcs lubviôft -cl from ha'f the fimi of the values of the twofinglelivcs thu is, h.ilr' the vhIul" ot the loi-gft of the two lives by pn;l-li-in IV. qf r.î. de Moivrc's Tieanle on Lile Annuiti'es. A iimilar dcmonflration may bs eafily applied to the filution of the other queilion.
1 hc beft rules for finding, in a'I cafés, the values of reverfions
(lepenilintr on furvivoifliips, are Mr. Simpfoa's, in his S:k«ft LxcK'id*, p. 2,97, &
âges