POSITION. 221 



2. Find how much the results are difFerent from the re- 

 sult in the question. 



3. Multiply each of the errors by the contrary supposi- 

 tion, and find the sum and difference of the products. 



4. If the errors be alike, divide the dIfFevence of the 

 products by the difference of the errors, and the quotient 

 will be the answer. 



5. If the errors be unlike, divide the sum of the prod- 

 nets by the sum of the errors, and the quotient will be 

 the answer. 



Note. The errors are said to be allkey when they are 

 both too great or both too little ; and U7jlikey when one is 

 too great and the other too little. 



EXAMPLES, 



1. A lady bought tabby at 4s. a yard, and Persian at 2s. 

 a yard ; the whole number of yards she bought was 8, and 

 the whole priuc u;uc. . Kow inauj j-ardo kad olic o£ cach 

 sort f 



Suppose 



extremes, rx — rhzzsx — sa ; and, by transposition, rx — siKz:zr!/ — sa ; 



aod, by division, xz= = number sought. 



r — s 



Again, if r and s be both negative, ws shall have — r : — s 

 ; : X — a : x — If, and therefore — rx-\-rh=z — sx-^-sa ; and rx— 



^.v=r3 — sa ; whence x == ■ as before. 



r — J- 



In like manner, if r or j be negative, we shall have sxrrr — ^ — , 

 by working as before, which is the rule. 



Note. It will be often advantageous to make 1 and o the 

 suppositions. 



