Question

How do you define a variable and write an expression for each phrase: one-third of the total of nine times a number and twenty one?

Answer 1

`3x+9`

Explanation:

You don't need to "define" a variable, if that is what you mean. A variable can be any letter - `x`, `r`, `d`, etc etc. But `x` is the most common, and so I shall stick to it here.

One third of the total of states that the "nine times a number and twenty one" comes before the one-third.

Since we defined "a number" to be `x`, then nine times `x` is simplify `9x`.

The "total of" is telling us to take the sum of `9x` and `21`. It is just simplify `9x+21`

And then it is asking us to take `1/3` of that. That is just dividing `9x+21` by `3`, as `9x+21*1/3=(9x+21)div3/1`. `9x` divided by `3`
is `3x`, and `27` divided by `3` is `9`.

Therefore we get `3x+9`