Virtually every student knows that the sum of the measures of the three angles of a triangle is 180 (and for those who don’t know this, the kind folks at the Educational Testing Service have listed this fact at the top of every SAT math section).
Consider this question: What is the average measure of one angle of a triangle? It’s a simple question. To find the average of any three things, we find the sum and then divide by 3. Since the sum of the three angles of a triangle is always 180, when we divide by 3 we find that the average measure of an angle of a triangle is always 60. This fairly simple fact has nice implications for SAT math problems.
Only an equilateral triangle has 3 angles that each measure exactly 60. If we then decrease one of the angles by one degree to 59, to balance this out one of the other angles must increase to 61 so that the average remains 60 (and the sum remains 180). Now we have three unequal angles. Let’s examine them more closely. What can be said about the smallest angle of a triangle? Setting aside the equilateral triangle situation, the smallest angle of a triangle must measure less than 60. Are there any other conclusions that we can draw about the other two angles of the triangle? The largest angle of the triangle must measure greater than 60. Is there anything we can state for sure regarding the “middle-sized” angle of a triangle? It may be more or less than 60, we can’t tell for sure. However, if you give it some further thought, could this angle be as large as 90 degrees? If the “middle-sized” angle of a triangle is 90 and then the largest angle is more than that, we would have more than 180 degrees. Therefore, the “middle-sized” angle must measure less than 90.
All of these conclusions derive directly from the simple fact that the sum of the measures of the angles of a triangle is 180. Make no mistake about it – the SAT will test you about these more in-depth concepts. Taking an SAT Prep Course will hone your math skills.



