+1678 Mr and Mrs. Wilson have 3 children: Jessica, Jeremy, and Jenna. The average of Jessica and Jeremy's age is $ 11$. The average of all three children's ages is $ 10$. How old is Jenna?
+1223 Let's label the children's ages:
Jessica = a
Jeremy = b
Jenna = c
(a + b)/2 = 11
(a + b + c)/3 = 10
From there, we can simplify:
a + b = 22 . (1)
a + b + c = 30 . (2)
Subtract equation (1) from (2) to get c = 8.
