The test have to be timed because you can not spend 30 minutes doing a question.And if you are at the super market and you add up how much money you need to pay and you take so long,the cashier might call ''NEXT!''.When you take a test,and you come to a question you do not understand,skip it,and go back to that question when you are finished with the whole test so you would not waste your time on only one little question before your teacher collects the test..