GATE CS 2025 Set 1 Q.3: Quantitative Aptitude

The average marks obtained by a class in an examination were calculated as $30.8$ . However, while checking the marks entered, the teacher found that the marks of one student were entered incorrectly as $24$ instead of $42$ . After correcting the marks, the average becomes $31.4$ . How many students does the class have?

$25$

$28$

$30$

$32$

Official answer and solution

Official answer: C
From: Official GATE 2025 answer key

Solution

Relate the net change in total marks to the net change in the class average.

Let $n$ be the number of students in the class. Correcting the student's score from $24$ to $42$ increases the total marks of the class by:

\Delta S = 42 - 24 = 18

This increases the class average by $\Delta \bar{x} = 31.4 - 30.8 = 0.6$ . Since $\Delta \bar{x} = \frac{\Delta S}{n}$ , we get:

n = \frac{18}{0.6} = 30

Final answer

Option (C)

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Source

Paper: GATE 2025 Computer Science and Information Technology - Session 1 (CS1)
Question: 3 of 65
Section: General Aptitude

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