Final answer:
An algebraic expression for the given phrase using 'x' as the unknown number is 3(x - 1), which represents taking 1 away from the number and then multiplying by 3.
Step-by-step explanation:
The algebraic expression for the phrase “I think of a number, take away 1 and multiply the result by 3”, using x as the unknown number, can be written as 3(x - 1). In this expression, you would first subtract 1 from the number you are thinking of, which is represented as x. After taking away 1, you multiply that result by 3 to complete the expression.
To explain this step-by-step: if x is your number, subtracting 1 can be represented algebraically as x - 1. Then, you multiply by 3, which is represented as 3(x - 1). This type of operation is fundamental in algebra, where we use letters to represent numbers, and it allows us to manipulate and solve equations systematically.