What is x when 81 divided by x equals 90?

To find the answer, just divide the dividend by the quotient: 81 ÷ 90 = 0.9

To prove this, let's compute 81 divided by 0.9: $\frac{81}{0.9} = 90$

How does it work?

Asking what the value of x could be when 81 divided by x gives a result of 90, is equivalent to solving the following equation:

$\frac{81}{x} = 90$

Multiply both sides by x: $\frac{81 x}{x} = 90 x$
$\frac{81 x}{x}$ is equivalent to $\frac{x}{x} \times 81$ , which simplifies to $1 \times 81$ (or just $81$ ).
Thus, the equation becomes: $81 = 90 x$
To find x, divide both sides by 90: $\frac{81}{90} = \frac{90 x}{90}$
Which gives, after simplification: $0.9 = x$ (or $x = 0.9$ )

So, if the dividend is 81 and the quotient is 90, the divisor is 0.9.