I think a number. If a substract 8 from it and multiply by 3, the result is 21?
Let's start by setting up an equation to represent the given information. Let the unknown number be represented by 'x'.
According to the information provided, "If I subtract 8 from it (the number) and multiply by 3, the result is 21." Mathematically, this can be expressed as:
3(x - 8) = 21.
Now, let's solve this equation to find the value of 'x':
3(x - 8) = 21
Divide both sides of the equation by 3:
(x - 8) = 7
Add 8 to both sides of the equation to isolate 'x':
x = 7 + 8
x = 15.
Therefore, the number you were thinking of is 15.