The sum of an unknown number and fifteen is decreased by eight. The result is two.

-5

Step-by-step explanation:

Let's call this unknown number x.

Then (x+15) - 8=2. Therefore, x=2+8-15 = - 5.

n+15 - 8 = 2

n=-5

Step-by-step explanation:

Let n be the unknown number

sum of an unknown number and fifteen

n+15

is decreased by eight

n+15 - 8

The result is two.

n+15 - 8 = 2

Combine like terms

n + 7 = 2

Subtract 7 from each side

n+7-7=2-7

n=-5