If a certain number is multiplied by five, the result is the  same as twenty-one plus twice the original number.  What is the value of the original number?
To solve for the original number, I need to set up an equation that represents the given information. Let x be the original number. Then, multiplying it by five gives 5x. Twenty-one plus twice the original number is 21 + 2x. The problem says that these two expressions are equal, so I can write the equation 5x = 21 + 2x. Now I need to isolate x on one side of the equation. I can do this by subtracting 2x from both sides, which gives 3x = 21. Then, I can divide both sides by 3, which gives x = 7. This means that the original number is 7. 