Susan is $6$ years old. Her sister is one year younger and her brother is one year older. What is the sum of the ages of the three siblings? 
Overseas Competition->Knowledge Point->Word Problem Modules->Age Problems->Basic Relationships in Age Problems
Susan\textquotesingle s sister is $6-1=5$ years old and her brother is $6+1=7$ years old. The sum of the ages of the three siblings is $5+6+7=18$. 