Answer:
66
Step-by-step explanation:
If there are <em>n</em> students, then the number of pairs is 
.
With 12 students, 
pairs can be formed.
The reason the formula works is this: Each of the 12 students can be paired with 11 other students (no student is paired with him/her self). But counting 12 x 11 = 132 counts each pair <u>twice</u>. Example: student A can be paired with student B,..., student B can be paired with student A. The pair was counted two times.
See the attached image that shows pairings of 5 students. There are
5(5 - 1)/2 = 5(4)/2 = 10 pairs.
1. Which polygon or polygons are regular?
A regular polygon is a polygon that is equiangular (all angles are equal in measure) and equilateral (all sides have the same length).
Therefore your answer is:
A. equilateral triangle
C. square
2. Which polygon is always irregular?
traingle - NOT (equilateral triangle)
trapezoid - YES
square - NOT
hexagon - NOT (regular hexagon)
Problem 10
You are correct. You divide 360 over the exterior angle measure to get 360/72 = 5
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Problem 11
x = 33 is correct as this angle is an alternate interior angle pair with the 33 degree angle up top
y = 38 is correct since y+33+109 = 180 solves to y = 38. In other words: 38+33+109 = 180
z = 109 is correct. The opposite angles of a parallelogram are congruent
