SAT Math Practice Exam

Answer C This is a simple algebraic equation with one variable x. Try to bring all terms with x on one side and all other terms on the other side of the equation.
3x -5 = 15 - x
3x + x = 15 +5
4x= 20 or x = 5
But the question asks for value of 3x which is 15 and not 5.

Key takeaway: To solve simple equations, use mathematical operations such as add, multiply to isolate the variable . Get the variable alone on one side of the equal sign