Patricia scored 80% on a math test. she missed 4 problems. how many problems were on the test?

There would be exactly twenty problems on the test for her to be able to get 80%.
You know it can't be ten because then that would make it 60% not 80% but if you add the first number of the percentage (8) and multiply it by two it will get you 16 then if you add 4 to that that would make it 20 and 16/20 equals 80%