human
I am three years younger than my brother, and I am 2 years older than my sister. My mom's age is one less than three times my brother's age. When you add all our ages, you get 87. How old am I?
assistant
Define a variable ** Let X be my age. My brother is X + 3 years old. My sister is X - 2 years old.
How old is my mom? ** My mom is (X + 3) * 3 - 1 years old.
Write an equation ** The sum of our ages is X + (X+3) + (X-2) + [(X+3)*3 - 1] = 87 years old.
Simplify ** Multiplying through the parentheses and combining like terms, you get X*6 + 9 = 87 years old.
Simplify ** Subtracting nine from both sides and dividing both sides by 6, you get X = 13 years old.
#### 13