Thomas has finished 4 problems of his weekly math homework. If he needs to solve a total of 20 problems, which of the following shows the equivalent of the percentage of his math homework Thomas still needs to complete?
Thomas has finished 4 out of 20 problems, so he still needs to complete 20 - 4 = <<20-4=16>>16 problems.
The percentage of his math homework Thomas still needs to complete is (16/20) * 100% = 80%. Answer: \boxed{80}.