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Q5·CSAT · Prelims 2026

Averages — Data Correction

NumericalAveragesArithmetic ProblemMedium

Question

The class average x in a test increases by 4 when the score of a student is rectified, whose corrected score is 100 instead of 0. Later, the score of another student was found to have been recorded as 81 in place of 56. If there are no other corrections and the final corrected average is y, then y-x is

Options

a

2

b

3

Answer
c

5

d

6

Explanation

Let n be the total number of students in the class.

First Correction Analysis: A student's score increases from 0 to 100, adding a net value of +100 to the class total. This adjustment causes the class average x to increase by 4.

100/n = 4 \implies n = 25 students

Second Correction Analysis: Another student's score was mistakenly recorded as 81 instead of 56. To correct this, we must subtract the error, resulting in a net change of 56 - 81 = -25 to the class total.
Combined Net Effect: The net change from both corrections to the total class score is 100 - 25 = +75.
Final Average Shift: The net shift between the final corrected average y and the initial uncorrected average x is given by dividing the total net change by the number of students:

y - x = 75/n = 75/25 = 3

The net shift in a group average is calculated by dividing the total net sum of all data corrections by the total number of individual entries.

Answer: (b).

Question details

Year

2026

Paper

CSAT

Question

Q5

Section

Quantitative Aptitude

Sub-topic

Averages

Type

Arithmetic Problem

Difficulty

Medium

Source hint

Standard averages — net change correction framework

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