Answer to Problem # 18:

P cents    =   3  x  C cents
       lb.                           lb.

In 1 lb. of nuts:  
 (1/3 lb.  x  P cents ) + ( 2/3 lb.  x    C cents )  =   40 cents
                            lb.                                    lb. 

(1/3 x P cents) + ( 2/3 x C cents )  =  40 cents  

 Substituting '3C' for 'P'

(1/3  x  3 C cents)  + (2/3  x  C cents)  =  40 cents 

1 C   +  2/3 C  =   1  2/3 C   =   40      or    5/3 C  =   40

C  =  40  x  3/5   =   120 / 5  =   24      P = 3 x C  =  72

                 Cashews =  24 cents / lb.  (ANSWER)   
                  Pecans =  72 cents / lb. (ANSWER)



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