2007 AMC 10A Problems/Problem 10
Problem
The Dunbar family consists of a mother, a father, and some children. The average age of the members of the family is , the father is
years old, and the average age of the mother and children is
. How many children are in the family?
Solution 1
Let be the number of children. Then the total ages of the family is
, and the total number of people in the family is
. So
Solution 2
Let be the number of the children + the mom. The father, who is
, plus the sum of the ages of the kids and mom divided by the number of kids and mom plus
(for the dad) =
. This is because the average age of the entire family is
This statement, written as an equation, is:
people -
mom =
children.
Therefore, the answer is
Solution 3
Let be the Mom's age.
Let the number of children be and their average be
. Their age totaled up is simply
.
We have the following two equations:
, where
is the family's total age and
(Mom + Dad + Children).
The next equation is , where
is the total ages of the Mom and the children, and
is the number of people.
.
We know the value for , so we substitute the value back in the first equation.
.
.
Earlier, we set to be the number of children. Therefore, there are
children.
See also
2007 AMC 10A (Problems • Answer Key • Resources) | ||
Preceded by Problem 9 |
Followed by Problem 11 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | ||
All AMC 10 Problems and Solutions |
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