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There is no such valid test, so I would definitely question it.
There really isn't a need to conduct a test to answer this question. There isn't even a problem to test for or a hypothesis to test, so there is no need to perform any kind of test for this question.
.8 x 30 = 24 so you can miss 6 questions
On a 22 question test, if you miss one question (wich can be written as 21/22 -- 21 divided by 22), you will have a 95.45, an A, according to a calculator. So, 100-95.45 (100 minus 95.45) is about 4.55: therefore, on a 22 question test, each question is worth about 4.55 points. :)
70% of 15 is 10.5 so it is 4.5 questions
80% of 70 is 56 so 14 errors/omissions max.
Each question is an independent event with 4 possibilities, so the possibilities are 48 = 65,536
IQ test questions are used to determine ones IQ. Many are growing or trick questions as some ones IQ does not change so the test is not based on memorization of facts.
One question in eight would be 12.5% of the test - if all the questions whereof equivalent difficulty.Tests often have some "hard" and some "easy" questions so the percentage of marks per question is not dependant on the ration of one question to the number of questions.
A prompt is a stimulus -- something that causes a person to respond. So a test essay prompt is an essay question on a test.
Test questions will be asked so that a teacher can know where a person stands, academically. This is important so that the student learns what is necessary to progress.
According to my grade calculator with a 60 question test your break point would be 30 for a D- and a 57 for an A+, so an 80% would 47 correct questions and that means you would get a B and that is missing 10 questions.