What is x when 51 divided by x equals 12?

To find the answer, just divide the dividend by the quotient: 51 ÷ 12 = 4.25

To prove this, let's compute 51 divided by 4.25: $\frac{51}{4.25} = 12$

How does it work?

Asking what the value of x could be when 51 divided by x gives a result of 12, is equivalent to solving the following equation:

$\frac{51}{x} = 12$

Multiply both sides by x: $\frac{51 x}{x} = 12 x$
$\frac{51 x}{x}$ is equivalent to $\frac{x}{x} \times 51$ , which simplifies to $1 \times 51$ (or just $51$ ).
Thus, the equation becomes: $51 = 12 x$
To find x, divide both sides by 12: $\frac{51}{12} = \frac{12 x}{12}$
Which gives, after simplification: $4.25 = x$ (or $x = 4.25$ )

So, if the dividend is 51 and the quotient is 12, the divisor is 4.25.