Andy and Benny have 80 books altogether. Benny and Colin have 70 books altogether. Andy and Colin have 90 books altogether. How many books does each of them hav

Question

please advise if equation is the only solution?

Answer 1

 

   A  +  B          =  80

           B  +  C  =  70

   A          +  C  =  90

--------------------------     [add three equations]

 2A + 2B  + 2C = 240

 

   A  +  B  + C  = 120          [divide by 2]

 

Now, to find any one variable, subtract the equation with the other two variables:

   A  +  B  +  C  = 120

           B  +  C  =   70

--------------------------

   A                  =   50

 

   A  +  B  +  C  = 120

   A          +  C  =   90

--------------------------

           B          =   30

 

   A  +  B  +  C  = 120

   A  +  B          =   80

-------------------------

                    C  =   40

 

Be sure to check the answers using the original equations. [This is the only solution.]