What is x when 81 divided by x equals 18?

To find the answer, just divide the dividend by the quotient: 81 ÷ 18 = 4.5

To prove this, let's compute 81 divided by 4.5: $\frac{81}{4.5} = 18$

How does it work?

Asking what the value of x could be when 81 divided by x gives a result of 18, is equivalent to solving the following equation:

$\frac{81}{x} = 18$

Multiply both sides by x: $\frac{81 x}{x} = 18 x$
$\frac{81 x}{x}$ is equivalent to $\frac{x}{x} \times 81$ , which simplifies to $1 \times 81$ (or just $81$ ).
Thus, the equation becomes: $81 = 18 x$
To find x, divide both sides by 18: $\frac{81}{18} = \frac{18 x}{18}$
Which gives, after simplification: $4.5 = x$ (or $x = 4.5$ )

So, if the dividend is 81 and the quotient is 18, the divisor is 4.5.