What is x when 51 divided by x equals 20?

To find the answer, just divide the dividend by the quotient: 51 ÷ 20 = 2.55

To prove this, let's compute 51 divided by 2.55: $\frac{51}{2.55} = 20$

How does it work?

Asking what the value of x could be when 51 divided by x gives a result of 20, is equivalent to solving the following equation:

$\frac{51}{x} = 20$

Multiply both sides by x: $\frac{51 x}{x} = 20 x$
$\frac{51 x}{x}$ is equivalent to $\frac{x}{x} \times 51$ , which simplifies to $1 \times 51$ (or just $51$ ).
Thus, the equation becomes: $51 = 20 x$
To find x, divide both sides by 20: $\frac{51}{20} = \frac{20 x}{20}$
Which gives, after simplification: $2.55 = x$ (or $x = 2.55$ )

So, if the dividend is 51 and the quotient is 20, the divisor is 2.55.