Answer: x-(x+1)
Explanation:
The number is our unknown here, so we'll use the variable x to represent it in the equation. Now, a key phrase here is "decreased by"; that's telling us to subtract whatever comes next, which in this case, is the sum of x and 1. Since we're instructed to subtract the sum of these numbers together, we want to go ahead and put x+1 in parentheses. Now we've got the basic elements of the equation figured out, we only have to put it all together! And that gives us x, which is the number, minus (x+1), which is the sum of that number and 1.