What is x when 86 divided by x equals 21?

To find the answer, just divide the dividend by the quotient: 86 ÷ 21 = 4.0952380952381

To prove this, let's compute 86 divided by 4.0952380952381: $\frac{86}{4.0952380952381} = 21$

How does it work?

Asking what the value of x could be when 86 divided by x gives a result of 21, is equivalent to solving the following equation:

$\frac{86}{x} = 21$

Multiply both sides by x: $\frac{86 x}{x} = 21 x$
$\frac{86 x}{x}$ is equivalent to $\frac{x}{x} \times 86$ , which simplifies to $1 \times 86$ (or just $86$ ).
Thus, the equation becomes: $86 = 21 x$
To find x, divide both sides by 21: $\frac{86}{21} = \frac{21 x}{21}$
Which gives, after simplification: $4.0952380952381 = x$ (or $x = 4.0952380952381$ )

So, if the dividend is 86 and the quotient is 21, the divisor is 4.0952380952381.