if 75 percent of a class answered the first question on a certain test correctly , 25 percent answered the second question on the test correctly , and 20 percent answered neither of the questions correctly , what percent answered both correctly ?
"{ total } = { first } + { second } - { both } + { neither } 100 % = 75 % + 25 % - { both } + 20 % - - > { both } = 20 % . answer : b ."
subtract(add(add(75, 25), 20), const_100)