Question counte
- Counterclockwise from top right, the lines are labeled s, r, q, and t.
- Line s intersects line r above line q.
- Line s and line r each intersect line q and line t.
- At the intersection of line s and line r, 1 angle is labeled counterclockwise from top as follows:
- Top: a/li>
- At the intersection of line s and line q, 1 angle is labeled counterclockwise from top-left as follows:
- Top left: b/li>
- At the intersection of line r and line t:
- The line segment divides the bottom-left angle into two equal angles, each labeled w/li>
- A note indies the figure is not drawn to scale.
In the figure, parallel lines and are intersected by lines and . If and , what is the value of ?
Counterclockwise from top right, the lines are labeled s, r, q, and t. Line s intersects
Hard-difficulty · SAT Math · Lines, Angles, and Triangles — Angle relationships (parallel lines). Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.
Answer explanation
The correct answer is . In the figure, lines , , and form a triangle. One interior angle of this triangle is vertical to the angle marked ; therefore, the interior angle also has measure . It's given that . Therefore, the interior angle of the triangle has measure . A second interior angle of the triangle forms a straight line, , with the angle marked . Therefore, the sum of the measures of these two angles is . It's given that . Therefore, the angle marked has measure and the second interior angle of the triangle has measure , or . The sum of the interior angles of a triangle is . Therefore, the measure of the third interior angle of the triangle is , or . It's given that parallel lines and are intersected by line . It follows that the triangle's interior angle with measure is congruent to the same side interior angle between lines and formed by lines and . Since this angle is supplementary to the two angles marked , the sum of , , and is . It follows that , or . Subtracting from both sides of this equation yields . Dividing both sides of this equation by yields . Note that 101/2 and 50.5 are examples of ways to enter a correct answer.
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