In math, what is the definition of "variable"?

In mathematics, a variable is a letter that represents any number. Therefore, variables are often used to represent unknown numbers.

For example, the image I attached is a jar filled with coins. We can use "X" to represent the number of coins in the jar since we don't know how many there are.

d. millimeters per hour.

step-by-step explanation:

we are given that,

carlo used a rain gauge to measure the amount of water his lawn is receiving from the sprinklers.

since, according to the options, we see that,

water cannot be measured by 'miles per hour', 'meters per second' and 'grams per seconds'.

we get that, the water can be measured by 'millimeters per hour'.

hence, the appropriate rate for describing the amount of water is 'millimeters per hour'.

the answer is c: divide the arc's degree measure by 360°, then multiply by the circumference of the circle.