What is x when 39 divided by x equals 10?

To find the answer, just divide the dividend by the quotient: 39 ÷ 10 = 3.9

To prove this, let's compute 39 divided by 3.9: $\frac{39}{3.9} = 10$

How does it work?

Asking what the value of x could be when 39 divided by x gives a result of 10, is equivalent to solving the following equation:

$\frac{39}{x} = 10$

Multiply both sides by x: $\frac{39 x}{x} = 10 x$
$\frac{39 x}{x}$ is equivalent to $\frac{x}{x} \times 39$ , which simplifies to $1 \times 39$ (or just $39$ ).
Thus, the equation becomes: $39 = 10 x$
To find x, divide both sides by 10: $\frac{39}{10} = \frac{10 x}{10}$
Which gives, after simplification: $3.9 = x$ (or $x = 3.9$ )

So, if the dividend is 39 and the quotient is 10, the divisor is 3.9.