GRE Math : How to find an angle in a parallelogram
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Example Questions
Example Question #11 : Quadrilaterals
In a given parallelogram, the measure of one of the interior angles is 25 degrees less than another. What is the approximate measure rounded to the nearest degree of the larger angle?
78 degrees
77 degrees
102 degrees
103 degrees
101 degrees
103 degrees
There are two components to solving this geometry puzzle. First, one must be aware that the sum of the measures of the interior angles of a parallelogram is 360 degrees (sum of the interior angles of a figure = 180(n-2), where n is the number of sides of the figure). Second, one must know that the other two interior angles are doubles of those given here. Thus if we assign one interior angle as x and the other as x-25, we find that x + x + (x-25) + (x-25) = 360. Combining like terms leads to the equation 4x-50=360. Solving for x we find that x = 410/4, 102.5, or approximately 103 degrees. Since x is the measure of the larger angle, this is our answer.
Example Question #2 : How To Find An Angle In A Parallelogram
Figure 
Quantity A: The largest angle of 
Quantity B:
Which of the following is true?
The two quantities are equal.
Quantity A is larger.
The relationship cannot be determined.
Quantity B is larger.
The two quantities are equal.
By using the properties of parallelograms along with those of supplementary angles, we can rewrite our figure as follows:
Recall, for example, that angle 
Now, you know that these angles can all be added up to 
Therefore, you can write:
Simplifying, you get:
Now, this means that:
Example Question #12 : Parallelograms
Figure 
What is 
Cannot be computed from the data given.
Because of the character of parallelograms, we know that our figure can be redrawn as follows:
Because it is a four-sided figure, we know that the sum of the angles must be 
Solving for 
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