2019 CSAT, all questions
UPSC Prelims 2019 · CSAT
Question 30: Basic Numeracy
P, Q and R are three towns. The distance between P and Q is 60 km, whereas the distance between P and R is 80 km. Q is in the West of P and R is in the South of P. What is the distance between Q and R ?
a140 km
b130 km
c110 km
d100 km
AnswerUPSC’s answer is (d).
Q is west of P and R is south of P, so the angle at P is a right angle. PQ = 60 and PR = 80, so QR is the hypotenuse of a right triangle: √(60^2 + 80^2) = √(3600 + 6400) = √10000 = 100 km. This is the 3-4-5 triangle scaled up by 20, which is a quick way to spot the answer.
Why each option is right or wrong
- (a) Wrong: 140 is PQ + PR, the path through P, not the straight line.
- (b) Wrong: 130 does not match the hypotenuse.
- (c) Wrong: 110 does not match the hypotenuse.
- (d) Right: a 60-80-100 right triangle.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2019, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.