Question 258316
(a+b)/2 = 10 (first equation)


(b+10)/2 = (c/2) (second equation)


first equation states that the average of a and b is 10.


second equation states that the average of b and 10 is c/2


question is what is the average of a and c.


take the second equation and solve for b.


second equation is:


(b+10)/2 = c/2


multiply both sides of this equation by 2 to get:


b + 10 = c


subtract 10 from both sides of this equation to get:


b = c - 10


substitute for b in the first equation.


first equation is:


(a+b)/2 = 10


multiply both sides of this equation by 2 to get:


a + b = 20


subsstitute (c-10) for b to get:


a + c - 10 = 20


add 10 to both sides of this equation to get:


a + c = 30


divide both sides of this equation by 2 to get:


(a+c)/2 = 15


average of (a+c) is equal to 15.