Prelims 2024

Q. Let p and q be positive integers satisfying p<q and p+q=k.
What is the smallest value of k that does not determine p and q uniquely?

a) 3
b) 4
c) 5
d) 6
Correct answer: c) 5

Question from UPSC Prelims 2024 CSAT Paper

Explanation:

p<q and p+q=k

Let’s approach this step-by-step:

1) First, let’s consider what it means for p and q to be determined uniquely. It means that for a given k, there’s only one possible pair of positive integers p and q that satisfy the conditions.

2) Now, let’s start with small values of k and see how many pairs of p and q we can find:

For k = 3:
p = 1, q = 2 (only possibility)

For k = 4:
p = 1, q = 3 (only possibility)

For k = 5:
p = 1, q = 4
p = 2, q = 3

3) We see that k = 5 is the first value where we have more than one possible pair of p and q.

The correct answer is c) 5.

UPSC All In One App
Get UPSC Prelims PYQ, Mains Model Answer, Test Series, Short Notes. Click to Install !!