Why is a number divided by 0 equal to infinity?

You cannot divide a number by zero. This is easily explained by a simple example with the reverse operation of division, which is multiplication.

For any nonzero number A, find the value of B such that A/0 = B

This means that there would have to be some number B such that B x 0 = A

and there is no such number by the law of multiplication by zero.

Likewise, even for the huge number ∞, you would have the expression

A/0 = ∞ and be faced with the impossible equation ∞ x 0 = A

While it is tempting to imagine infinity as the inverse of zero, this is not the case. Zero is a defined value, while infinity is not.