The average age of the three Wilson children is 7 years. If the two younger children are 4 years old and 7 years old, how many years old is the oldest child?
I know that to find the average of three numbers, I need to add them up and divide by three. So, if the average age is 7, that means that the sum of the ages must be 7 times 3, or 21. I also know that the two younger children are 4 and 7, so I can subtract their ages from the sum to get the age of the oldest child. That is, 21 - 4 - 7 = 10. Therefore, the oldest child is 10 years old. 