"triple a number decreased by 5 feet."

3(x-5)? check that.

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To write the algebraic expression for "triple a number decreased by 5 feet," we can break it down into three steps:

1. Start with a variable representing "a number." Let's use the variable "x."

2. Triple the value of the number. To do this, multiply the variable "x" by 3.

3. Finally, subtract 5 feet from the tripled value. You can express this by subtracting 5 from the result of step 2.

Putting all of this together, the algebraic expression for "triple a number decreased by 5 feet" is 3x - 5.