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 x be number of children+the mom. The father, who is 48, plus the number of kids and mom divided by the number of kids and mom plus 1 (for the dad)=20. This is because the average age of the entire family is 20. Basically, this looks like 48+16x/x+1=20
7 people - 1 mom = 6 children.
E is the answer
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 | |
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All AMC 10 Problems and Solutions |
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