Final answer:
An expression to show h decreased by 13 is written as h - 13. This denotes subtracting 13 from the value of h.
Step-by-step explanation:
To express the concept of h decreased by 13 in mathematical terms, you would write the expression h - 13. This simply means that you take the variable h, which represents some number, and subtract 13 from it.
The use of the minus sign (-) indicates the decrease, implying that whatever value h has, you will end up with a value that is 13 less.