Fill in the blank, _______ % of 50 = 40.

Correct option is B

Given:

_____% of 50 = 40

Solution:

Let the unknown percentage be $$x$$.

​$$x$$% of 50 = 40

$$\dfrac {x}{100}×50 = 40$$

$$x=\dfrac{40×100}{50} = 80$$

Therefore, the unknown percentage is 80.

Thus, the correct option is B.