Coding-Decoding MCQs for UPSC Prelims

Correct answer: C - Q is the father of P.

Read the expression left to right using the defined operators. 'P + R' means P is the son of R, so R is a parent of P. 'R - Q' means R is the wife of Q. So R is the wife of Q and R is P's mother (a parent), which makes Q the husband of R and therefore the father of P. Hence (c) Q is the father of P. The official UPSC answer key marks this (c).

Correct answer: C - Two

INCOMPREHENSIBILITIES has 21 letters with counts: I x 5, E x 3, N x 2, S x 2, and one each of C, O, M, P, R, H, B, L, T. In reverse alphabetical order the word becomes T S S R P O N N M L I I I I I H E E E C B, so the block of five I's occupies positions 11 to 15. In the original word, I's sit at positions 1, 13, 15, 17 and 19; comparing position by position, only positions 13 and 15 hold an I in both arrangements, and no other letter lands on its original position. So exactly two positions are unchanged - option (c). 'None' (a) misses the overlapping I block, 'One' (b) catches only one of the two coincidences, and 'Three' (d) overcounts.

Correct answer: D - 6

P = 4. The difference between P and T is 5, so T = 4 + 5 = 9 (4 - 5 = -1 is not in the 1 to 9 range). The difference between N and T is 3, so N = 9 - 3 = 6 (9 + 3 = 12 is out of range). Hence N = 6.

Correct answer: B - T

Reversing each block of 4 letters and swapping Y and Z gives the new order: DCBA HGFE LKJI PONM TSRQ XWVU ZY. Counting along this arrangement, the 13th letter is P (the blocks contribute 4 letters each, so positions 13-16 are P, O, N, M). The fourth letter to the right of position 13 is the letter at position 17, which is T - option (b). Option (a) N is at position 15, option (c) H is at position 5, and option (d) I is at position 12, so none of them fits.

Correct answer: B - 2

From Q - S = 2S we get Q = 3S. Within {4, 5, 10, 12, 15} the possibilities are S = 4, Q = 12 or S = 5, Q = 15. Case S = 4, Q = 12: T = R + S + 3 = R + 7 with R, T from {5, 10, 15}; no pair works (5 + 7 = 12 is taken, 10 + 7 = 17 and 15 + 7 = 22 are not in the set). Case S = 5, Q = 15: T = R + 8 with R, T from {4, 10, 12}; only R = 4, T = 12 works, leaving P = 10. Then P + R - T = 10 + 4 - 12 = 2. The assignment is unique, so the value is 2.

Correct answer: D - 246

Read each three-letter block as the concatenation of its letter numbers, then double it. G=7, H=8, I=9 gives '789', and 789 x 2 = 1578. D=4, E=5, F=6 gives '456', and 456 x 2 = 912. Applying the same rule, A=1, B=2, C=3 gives '123', and 123 x 2 = 246. So ABC = 246.

Correct answer: A - CCIDD

Apply a backward shift equal to each letter's position in the word. MUMBAI: M(-1)=L, U(-2)=S, M(-3)=J, B(-4)=X, A(-5 wrapping) gives V, I(-6)=C, so M U M B A I -> L S J X V C, which matches. Use the same rule on DELHI: D(-1)=C, E(-2)=C, L(-3)=I, H(-4)=D, I(-5)=D, giving CCIDD. Other options do not follow the position-based backward shift, so they fail.

Correct answer: D - Neither 1 nor 2

Decode the symbols: P is >, Q is <, R is <= (not greater than), S is >= (not less than), T is =. Statement 1: 2x >= 3y multiplied by 3 gives 6x >= 9y; 3x = 4z multiplied by 2 gives 6x = 8z. So 9y <= 6x = 8z, i.e. 9y <= 8z, which means 9y > 8z can never be concluded; Statement 1 is incorrect. Statement 2: x < 2y and y <= z give only x < 2z, not x <= z. Counterexample: y = 1, z = 1, x = 1.5 satisfies x < 2y and y <= z, but x <= z fails since 1.5 > 1. Statement 2 is also incorrect. Hence neither statement is correct.