SIMPLE ADDITION; t^ 



3. Add this last found number and the uppermost line 

 together^ and if their sum be the same as that found by 

 the first addition, the sum is right. 



4* Add 8635, 2194, 7421, 5063, 21963 and 1245 to- 

 gether. Ans. 26754. 



5. Add 



the sUm of the former excesses, it is plairi this last excess must be 

 equal to the excess of nines contained in the total sam of all these 

 numbers ; the parts being equal to the whole. 



This rule was first given by Dr. Wall is, in his Arithmetic, 

 published A. D. 1657, and is a very simple easy method ; thouaii 

 it is liable to this inconvenience, that a wrong operation may some- 

 times appear to be right ; for if we change the places of any two 

 figures in the sum* it will Still be the same ; but then a true sum 

 will always appear to^ be true by this proof ; and to make a false 

 one a^jpear true, there must be at least two errors, and these op- 

 posite to each other ; and if there be more than two errors, they 

 must balance among themselves : but the chance against this 

 particular circurast;mce is so great, that wc may pretty safely Vu€t 

 to this proQf. 



c 



