UPSC (Prelims) 2026 Logical Reasoning Previous Year Questions

If ZERO is encoded as ADSN, then how do you encode STOP?

Seven cubes are identical in shape. Out of these, the weight of each of the six cubes is equal and the weight of the remaining cube is less than the weight of any other cube. A balance is used to identify the lightest cube. What is the minimum number of attempts required to distinguish the odd cube with certainty?

Eight persons P, Q, R, S, T, U, V and W sit around a round table in eight different seats placed with equal distance between any two consecutive seats. Both P and R are adjacent to Q. Both T and R are adjacent to S. Both U and W are adjacent to V. S and W are on opposite chairs. If while going in the clockwise direction around the table from P, one meets R before T, then how many persons shall Q cross while moving in the clockwise direction around the table before meeting W?

A pattern formed by two characters a and b is repeated more than once in the following string:

x b x a x a x x a x a x b a b

What is the pair in the 7th and 8th positions from the left in the above string?

P, Q, R, S and T are ranked $1$ to $5$ (not necessarily in that order). The rank of P is $4$, the rank of Q is not $5$, the rank of R is $1$, the rank of S is not $2$, the rank of T is not $3$. Then which of the following is/are correct?

I. If the rank of S is $3$, then that of T is $2$.
II. If the rank of Q is $3$, then that of T is $5$.

Select the answer using the code given below.

Two identical straight rods are painted in five distinct colours so that each of them gets divided into five equal parts along the length. In one of them, the portions are marked $P_1,P_2,P_3,P_4$ and $P_5$ (not necessarily in that order) whereas in the other, they are marked $Q_1,Q_2,Q_3,Q_4$ and $Q_5$ (not necessarily in that order). When the rods are kept parallel to each other side by side, $P_1$ and $Q_3$ match, $P_4$ matches $Q_1$ or $Q_2$, and $Q_4$ matches $P_3$ or $P_5$. If $Q_3$ and $Q_5$ are adjacent, which of the following is/are possible?

I. $Q_3$ is marked at the middle portion of the straight rod.

II. $P_2$ is marked at one of the extreme portions of the straight rod.

Select the correct answer using the code given below:

Seven persons $A,B,C,D,E,F$ and $G$ travel by three cars $X,Y,Z$. $A$ and another two of them travel by $X$. Only $E$ travels with $G$. $C$ travels by $Z$, but $B$ does not travel by $Y$. Besides, $A$ and $B$ do not travel by the same car. Then which of the following are correct?

I. No one travels alone.

II. Only $D$ travels with $F$.

III. Only $C$ travels with $B$.

Select the answer using the code given below:

There are four statements $X,Y,Z$ and $W$. Their relations are as follows:

If $X$ is incorrect, then so is $Z$; if $Y$ is incorrect, then $W$ is correct; if $W$ is correct, then $X$ is incorrect.

Which of the following is/are correct?

I. If $X$ is correct, then so is $Y$.

II. If $Z$ is correct, then it is not necessary that $Y$ is correct.

Select the answer using the code given below:

P has a son and a daughter. S is the mother of T. S is R's spouse. Q and R are children of P. Then how is Q related to S?

Consider the following statements :

Every red is blue. Every blue is green. Every green is yellow.

Which of the following statements denoted by P, Q and R are correct?

P. Every blue is yellow.

Q. Every red is green.

R. Every red is yellow.

Select the answer using the code given below.

A person facing the East travels 4 km straight and then turns right and travels 3 km, then further turns left and travels 2 km and finally turns left and travels 3 km. The minimum distance between the final point and the initial point, and the direction in which the person is facing at the final point are, respectively