Math Problems With Only Two Outcomes

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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