SAT Video Friday Math Challenge Question - Number of Numbers

Don’t take the long way The SAT is testing how you think, not how fast you can write. Yet students often do a question the long way, writing out as many numbers as possible. Instead, rely on logic and formulas, when applicable. Let’s take a look at the following question: How many numbers less than 100 are not divisible by 3? Instead of writing out all the numbers and then crossing out the ones that are not divisible by 3, find a way to identify the numbers that are divisible by 3. The best way to do this is by finding the highest number less than 100 that is divisible by 3. 99 should jump out at you. Since every third number up to 99 is divisible by 3, we can divide 99 by 3 (giving us 33) to find the number of numbers less than 100 that ARE divisible by 3. To answer the question subtract 33 from 99 (99 – 33 = 66). Remember: do not include 100, since the question asks for how many numbers less than 100. Now, let try a harder question, the SAT Challenge Question. The Challenge Question How many digits less than 1,000 are divisible by 3 and 5, but not by 7? After youve watched the video for the explanation, leave me any comments or questions you have below! 🙂