EULEE. 257 



annually besides, until both are dead. He investigates the re- 

 lation which must then hold between x, z and the sum to be 

 ensured. Thus a calculator may assign an arbitrary value to two 

 of the three quantities and determine the third. He may sup- 

 pose, for example, that the sum to be ensured is 1000 Rubles, 

 and that x = 0, and find z. 



Euler does not himself calculate numerical results, but he 

 leaves the formulae quite ready for application, so that tables 

 might be easily constructed. 



17 



