SOLUTION: Hannah has three sisters. The average age of her three sisters is 25. One sister is 26 years old and another is 21 years old. How old is Hannah's other sister?

Question 969848: Hannah has three sisters. The average age of her three sisters is 25. One sister is 26 years old and another is 21 years old.
How old is Hannah's other sister?
Answer by erica65404(394) (Show Source): You can put this solution on YOUR website!
average equals the sum of the values divided by the number of values.
This equal can be looked at as
where a is average, s is sum, and n is the number of values.
For example there are 3 sisters. that means 3 age values so n will be 3.
The average age of the sisters is 25, that is a.
and the sum of the sisters ages is 26 + 21 + x where x is the unknown age of the third sister.

solve for x

The third sisters age is 28.
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