Question

How do you define a variable and write an expression for each phrase: the sum of 13 and twice a number?

Answer 1

2x + 13

Explanation:

The reason for this is because, well, you kinda gotta go backwards. Twice an unknown number, and unknown number being a variable (by definition) would leave it as x, and twice of x is 2x.

And to finish off, since it's the sum with 13, and since sum means addition, it would end it with 2x + 13.

Answer 2

A variable is something that can change and/or is unknown.

Explanation:

sum = + or addition
a number = a variable or unknown value.
twice = `2 xx` or multiply by 2
13 = 13

(2n) = twice the unknown number

`( 13 + 2n)` is the algebraic expression for the phase

the sum of thirteen and w twice a number