(12) \( 15=\ldots \times 15 \)

To solve \( 15 = \ldots \times 15 \), we can find the missing number by rearranging the equation. Dividing both sides by 15 gives us \( 1 = \frac{\ldots}{15} \), which indicates that the missing number is simply 1. So we can fill in the blank: \( 15 = 1 \times 15 \). It's like a fun little magic trick of numbers where anything multiplied by 1 remains unchanged! In the world of mathematics, this property of 1 being the multiplicative identity is super important! Just like a trusty sidekick, whenever you’re solving equations or working with multiplication, you know that throwing a 1 into the mix keeps everything balanced. So the next time you're crunching numbers, remember: in the land of multiplication, 1 is a true hero!