What is the number of logically possible orders of all six cousins in terms of increasing age ?
a1
b2
c3
d4
AnswerUPSC’s answer is (b).
Using the same working: E = 22, A = 21, C = 20 and F = 18 are fixed. B and D take 17 and 19 in either order, as both fit the clues (A is older than B, C is older than D). So the orders of increasing age are B, F, D, C, A, E and D, F, B, C, A, E. That is 2 possible orders.
Why each option is right or wrong
(a) Wrong: B and D can swap places at 17 and 19.
(b) Right: B-F-D-C-A-E and D-F-B-C-A-E.
(c) Wrong: only two arrangements fit.
(d) Wrong: only two arrangements fit.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
