Which variable expression represents the phrase "the sum of a number and 10"?

10n

n-10

n:10

n + 10

let the given number is n

sum means use add (+) sign.

then sum of a number and 10 can be written as (n+10)

Hence (n+10) is the final answer.

Since each answer is 10 using a different action, here is what each one will give you.

Addition gives a sum. subtraction gives a difference, division gives a quotient and multiplication gives a product. It is asking for a sum, so which uses addition.