If a number is multiplied by 4 and then decreased by 5, the result is 15. What is the number?

To solve the problem, let's start by setting up an equation based on the description given.

Let the unknown number be represented by ( x ). According to the problem, when this number is multiplied by 4, and then decreased by 5, the result is 15. This can be expressed in the equation:

[ 4x - 5 = 15 ]

To find ( x ), we need to isolate it. First, we add 5 to both sides of the equation:

[ 4x - 5 + 5 = 15 + 5 ]

[ 4x = 20 ]

Next, we divide both sides of the equation by 4 to solve for ( x ):

[ x = \frac{20}{4} ]

[ x = 5 ]

Thus, the solution shows that the number is 5, which corresponds to the answer provided. This reasoning confirms that when 5 is multiplied by 4, it gives 20, and reducing that result by 5 returns 15, thus validating the operations described in the problem. This is why the answer is correct.