UPSC Prelims 2015 · CSAT
Question 76: Basic Numeracy
In a plane, line X is perpendicular to line Y and parallel to line Z; line U is perpendicular to both lines V and W; line X is perpendicular to line V. Which one of the following statements is correct ?
AnswerUPSC’s answer is (d).
In a plane, two lines perpendicular to the same line are parallel. X is perpendicular to both Y and V, so Y and V are parallel. U is perpendicular to both V and W, so V and W are parallel. Hence Y, V and W are all parallel. Z is parallel to X, and U is parallel to X (both perpendicular to V), so Z and U are parallel to each other but perpendicular to W.
Why each option is right or wrong
- (a) Wrong: Z and U are parallel but W is perpendicular to U.
- (b) Wrong: X is perpendicular to Y and V, so X is not parallel to them.
- (c) Wrong: V is parallel to W, not perpendicular.
- (d) Right: Y and W are both parallel to V, so Y, V and W are parallel.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2015, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.