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

May 17, 2018

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.

May 17, 2018

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

#### Explanation:

sum = + or addition
a number = a variable or unknown value.
twice = $2 \times$ or multiply by 2
13 = 13

(2n) = twice the unknown number

$\left(13 + 2 n\right)$ is the algebraic expression for the phase

the sum of thirteen and w twice a number