What is x when 78 divided by x equals 15?

To find the answer, just divide the dividend by the quotient: 78 ÷ 15 = 5.2

To prove this, let's compute 78 divided by 5.2: $\frac{78}{5.2} = 15$

How does it work?

Asking what the value of x could be when 78 divided by x gives a result of 15, is equivalent to solving the following equation:

$\frac{78}{x} = 15$

Multiply both sides by x: $\frac{78 x}{x} = 15 x$
$\frac{78 x}{x}$ is equivalent to $\frac{x}{x} \times 78$ , which simplifies to $1 \times 78$ (or just $78$ ).
Thus, the equation becomes: $78 = 15 x$
To find x, divide both sides by 15: $\frac{78}{15} = \frac{15 x}{15}$
Which gives, after simplification: $5.2 = x$ (or $x = 5.2$ )

So, if the dividend is 78 and the quotient is 15, the divisor is 5.2.