A can finish a task in 16 days and B can finish the same task in one fourth the time taken by A. Working together, what part of the same task can they finish in a day?

Correct option is C

Given:
A can finish the task in 16 days.
B can finish the same task in one- fourth the time taken by A, so B can finish the task in 4 days.
Formula Used:
​$$\text{Work done in one day} = \frac{1}{\text{Time taken to finish the task}}$$​​
Solution:
A's rate = $$\frac 1 {16}$$​ of the task per day

B's rate = $$\frac 1 {4}$$​ of the task per day
Total work done by A and B together in one day = $$\frac 1 {16} +\frac 1 {4} =\frac 5 {16}$$​
Thus, A and B together can finish $$\frac{5}{16}$$​ of the task in one day.