Let n = "a number." We will use this to translate the words into an equation.
"A number decreased by 5" becomes n - 5
"A number times 3" becomes 3*n or 3(n) or 3n. I'm going to use the last one.
Now set them equal like the problem asks.
n - 5 = 3n
Subtract 3n from both sides and add 5 to both sides to get constants on one side of the equal sign and variables on the other:
n - 3n = 5
Combine like terms:
- 2n = 5
Divide both sides by - 2 to isolate the variable:
n = 5 / -2
Your number is [tex] -\frac{5}{2} [/tex]
