其它
A movie ticket costs $17$ dollars and the tax is $a$ dollars. George purchases a movie ticket and writes on his ledgar : " the ticket cost $17+a$ dollars". Is this description accurate? 
Overseas Competition->Knowledge Point->Calculation Modules->Basic Concepts of Equation->Equivalent Substitution->Algebraic Expressions
When writing an algebraic expression with units, we need to write it in parentheses. 