What is really needed is the distance from each grade to the mean not the difference. You could take the absolute value of each difference and then calculate the mean. This is called the mean deviation, i.e. mean deviation = , where n is the number of students in the class. For class 1 this is 64/5 = 12.8.
1. Determine if there is a roof leak. Look for mold or mildew in attics or on walls. Look for discoloration on ceiling tiles or drywall. Look for wet, moist and rotting wood in crawl spaces, around chimneys or other additions, such as skylights and vents.. Check the attic for dyed areas. Follow the dye path from where it begins to where it comes out to find the leak. There may be multiple points of entry, so if you find one point, continue to search thoroughly until you are satisfied that there are no more leaks.
HOW IT WORKS. 1  The portable, hand-operated PosiTest AIR Leak Tester tests the air barrier integrity of single, two-ply and liquid membrane systems, including air barriers, roofing systems, waterproofing and ground liners by locating leaks. 2  In accordance with ASTM E1186, the PosiTest AIR will indicate whether leaks exist in the test area.