Write the following phrase as a variable expression. Use $x$ to represent "a number". eight decreased by thirteen times a number eight decreased by thirteen times a number is

Step 1 ：Translate the phrase 'eight decreased by thirteen times a number' into a mathematical expression. The word 'decreased by' suggests subtraction, and 'thirteen times a number' suggests multiplication.

Step 2 ：Therefore, the phrase can be written as \(8 - 13x\), where \(x\) represents 'a number'.

Step 3 ：Final Answer: The variable expression for the phrase 'eight decreased by thirteen times a number' is \(\boxed{8 - 13x}\).