Practice GMAT Data Sufficiency Question
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In triangle ABC, what is the measurement of angle C?
 The sum of the measurement of angles A and C is 120
 The sum of the measurement of angles A and B is 80
Correct Answer: B
 Since the sum of the measure of the interior angles of a triangle equals 180 degrees, you can write the following equation:
The measure of angles A + B + C = 180 
Evaluate Statement (1) alone.
 Translate Statement (1) into algebra:
A + C = 120  Use the foundational triangle equation (i.e., all angles add up to 180):
A + B + C = 180
(A + C) + B = 180
Substitute A + C = 120 into the equation.
120 + B = 180
B = 60  It is impossible to determine the value of angle C. Angle A could be 60 degrees and angle C could be 60 degrees. However, angle A could be 20 degrees and angle C could be 100 degrees.
 Statement (1) is NOT SUFFICIENT.
 Translate Statement (1) into algebra:

Evaluate Statement (2) alone.
 Translate Statement (2) into algebra:
A + B = 80  Use the foundational triangle equation (i.e., all angles add up to 180):
A + B + C = 180
(A + B) + C = 180
Substitute A + B = 80 into the equation.
80 + C = 180
C = 100  Statement (2) is SUFFICIENT.
 Translate Statement (2) into algebra:
 Since Statement (1) alone is NOT SUFFICIENT and Statement (2) alone is SUFFICIENT, answer B is correct.
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