How do you solve for r in $ K = \dfrac{{ar}}{p} $ ?

Hint: Here we will use the basic mathematical simplification and do cross – multiplication and will make the required term “r” the subject and write all the terms on the other sides.

Complete step-by-step answer:
Take the given expression: $ K = \dfrac{{ar}}{p} $
Do cross multiplication, where the denominator of one side is multiplied with the numerator of the opposite side.
 $ \Rightarrow Kp = ar $
The above equation can be re-written as –
 $ \Rightarrow ar = Kp $
Term multiplicative on one side if moved to the opposite side then it goes to the denominator.
 $ \Rightarrow r = \dfrac{{Kp}}{a} $
This is the required solution.
So, the correct answer is “ $ \Rightarrow r = \dfrac{{Kp}}{a} $ ”.

Note: Always remember that in cross multiplication, the numerator of one side is multiplied with the denominator of the opposite side and vice – versa. Always remember when you move any term from one side to another, then the sign of the term also changes. Positive term becomes the negative term and the negative term becomes the positive term. Constants are the terms with the fixed value while the variables are the terms which are unknown.