[ Arithmetic operations. Numerical identities ]

Malvina asked Buratino to multiply a number by 4 and add 15 to the result, but Buratino multiplied the number by 15 and then added 4, and yet, the answer was correct. What was the number?
Try to form an equation

## Solution

Let the unknown number be $x$ and write the equation: $4 x + 15 = 15 x + 4$. Solving this equation, we get: $11 = 11 x$, or $x = 1$.