What is x when 77 divided by x equals 21?

To find the answer, just divide the dividend by the quotient: 77 ÷ 21 = 3.6666666666667

To prove this, let's compute 77 divided by 3.6666666666667: $\frac{77}{3.6666666666667} = 21$

How does it work?

Asking what the value of x could be when 77 divided by x gives a result of 21, is equivalent to solving the following equation:

$\frac{77}{x} = 21$

Multiply both sides by x: $\frac{77 x}{x} = 21 x$
$\frac{77 x}{x}$ is equivalent to $\frac{x}{x} \times 77$ , which simplifies to $1 \times 77$ (or just $77$ ).
Thus, the equation becomes: $77 = 21 x$
To find x, divide both sides by 21: $\frac{77}{21} = \frac{21 x}{21}$
Which gives, after simplification: $3.6666666666667 = x$ (or $x = 3.6666666666667$ )

So, if the dividend is 77 and the quotient is 21, the divisor is 3.6666666666667.