Official Solution:This year, the combined age of the Perkins family members is 78 years. The family consists of four members: a husband, a wife, a daughter, and a son. The husband is 4 years older than the wife. The daughter is 2 years older than the son. If the husband's age is 7 times that of the son, how old is the daughter? A. 5
B. 7
C. 10
D. 13
E. 14
The plug-in method is the most efficient approach for this question.
Let's start with answer choice C:
If the daughter is 10 years old, then: the son is \(10-2=8\) years old. This means the husband is \(7*8=56\) years old, and the wife is \(56-4=52\) years old. Their combined age is \(10+8+56+52=126\), which is greater than 78. Thus, the daughter's age must be less than 10 years. We can also eliminate choices D and E.
Now, let's consider answer choice B:
If the daughter is 7 years old, then: the son is \(7-2=5\) years old. This implies the husband is \(7*5=35\) years old, and the wife is \(35-4=31\) years old. Their total age comes to \(7+5+35+31=78\). This matches the given sum, so it's the correct answer.
Answer: B