Recognizing when there are only two possible outcomes to an SAT Math Problem will save time and the potential for errors in calculation. For example, if 30% of books are on sale, then 70% of the books are not on sale. If 2/5th of the students in Mrs. Smith’s kindergarten class are girls, then you must immediately realize that 3/5th of Mrs. Smith’s kindergarten class are boys. If it rains 3 out of 5 days in a month, then it did not rain 2 out of 5 days in that month.
This binomial logic also helps with problems involving discounting. Understand that 20% off the existing price is the same as 80% of the original price. The natural tendency is to figure out what the 20% discount is and then subtract this amount from the original price. This involves two calculations, extra time and the potential to make a careless mistake. Why not just multiply the original price by .80?
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