What is x when 51 divided by x equals 5?

To find the answer, just divide the dividend by the quotient: 51 ÷ 5 = 10.2

To prove this, let's compute 51 divided by 10.2: $\frac{51}{10.2} = 5$

How does it work?

Asking what the value of x could be when 51 divided by x gives a result of 5, is equivalent to solving the following equation:

$\frac{51}{x} = 5$

Multiply both sides by x: $\frac{51 x}{x} = 5 x$
$\frac{51 x}{x}$ is equivalent to $\frac{x}{x} \times 51$ , which simplifies to $1 \times 51$ (or just $51$ ).
Thus, the equation becomes: $51 = 5 x$
To find x, divide both sides by 5: $\frac{51}{5} = \frac{5 x}{5}$
Which gives, after simplification: $10.2 = x$ (or $x = 10.2$ )

So, if the dividend is 51 and the quotient is 5, the divisor is 10.2.