Suppose t is the total time of examination.
As mentioned, Abdul finished exam 1/5 time of total time and Vishal finished the same 1/4 time earlier.
time taken by vishal to complete exam= t - t/4 = 3t/4 = 0.75t
time taken by Abdul to complete exam= t - t/5 = 4t/5 = 0.8t
As you can clearly see that Abdul has taken more time to finish exam.