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Saturday, 31 October

JEE Main · Maths · Statistics

Correcting Incorrect Variance

JEE Main asked Correcting Incorrect Variance 10 times in 10 of the 108 shifts Lumi analysed, in 2020, 2021, 2022, 2023, 2024 and 2025. It belongs to Variance and SD, in Statistics (Maths). The longest wait between two years asking it was 1 year. In 2022 and 2023 it came in more than one shift of the same year.

Updated 2026-10-24

Times asked
10
in 10 shifts
Years
6 of 8
First asked
2020
last in 2025
Pattern
Asked most years
across the analysed shifts

Questions on this idea a shift, by year

2017–2026. Asked in 2020, 2021, 2022, 2023, 2024 and 2025. Years differ in how many shifts Lumi analysed, so each year is scaled to one shift of 25 Maths questions.

00.150.30’170.08’200.03’210.11’220.21’230.05’240.13’250’26

Raw count: 2017: 0 in 1 shift · 2020: 1 in 12 shifts · 2021: 1 in 24 shifts · 2022: 3 in 24 shifts · 2023: 3 in 12 shifts · 2024: 1 in 18 shifts · 2025: 1 in 8 shifts · 2026: 0 in 9 shifts.

Shift by shift

Each square is one analysed shift, in date order. Open a filled one for that paper.

  • 20260 of 9
  • 20251 of 8
  • 20241 of 18
  • 20233 of 12
  • 20223 of 24
  • 20211 of 24
  • 20201 of 12
  • 20170 of 1

Asked in that shift More than once Not asked

How JEE Main framed it

Single correct is the usual form. Skill tested: calculation.

  • Find unknown data from mean and variance
  • Corrected mean and sd after mistaken observation

Difficulty

Easy 7Medium 3Hard 0

3 of the 10 questions had a numerical answer.

Every question

All 10 questions

From the official JEE Main shift papers, newest first. Open one for the full question, the options and the official answer.

  1. 7 Apr 2025, Shift 1 · Q9The mean and standard deviation of 100 observations are 40 and 5.1, respectively. By mistake one observation is taken as 50 instead of 40.…EasySingle correct
  2. 6 Apr 2024, Shift 1 · Q18The mean and standard deviation of 20 observations are found to be 10 and 2, respectively. On rechecking, it was found that an observation…EasySingle correct
  3. 15 Apr 2023, Shift 1 · Q19The mean and standard deviation of 10 observations are 20 and 8 respectively. Later on, it was observed that one observation was recorded…EasySingle correct
  4. 13 Apr 2023, Shift 2 · Q29The mean and standard deviation of the marks of 10 students were found to be 50 and 12 respectively. Later, it was observed that two marks…EasyNumerical value
  5. 8 Apr 2023, Shift 2 · Q18Let the mean and variance of 12 observations be 92\frac{9}{2} and 44 respectively. Later on, it was observed that two observations were…MediumSingle correct
  6. 28 Jun 2022, Shift 1 · Q23The mean and standard deviation of 15 observations are found to be 8 and 3 respectively. On rechecking it was found that, in the…EasyNumerical value
  7. 26 Jun 2022, Shift 2 · Q17The mean and standard deviation of 50 observations are 15 and 2 respectively. It was found that one incorrect observation was taken such…MediumSingle correct
  8. 27 Jul 2022, Shift 1 · Q22The mean and variance of 10 observations were calculated as 15 and 15 respectively by a student who took by mistake 25 instead of 15 for…EasyNumerical value
  9. 26 Aug 2021, Shift 1 · Q80The mean and standard deviation of 20 observations were calculated as 10 and 2.5 respectively. It was found that by mistake one data value…MediumSingle correct
  10. 8 Jan 2020, Shift 2 · Q68The mean and variance of 20 observations are found to be 10 and 4, respectively. On rechecking, it was found that an observation 9 was…EasySingle correct

Shifts: 8 Jan 2020, Shift 2, 26 Aug 2021, Shift 1, 26 Jun 2022, Shift 2, 28 Jun 2022, Shift 1, 27 Jul 2022, Shift 1, 8 Apr 2023, Shift 2, 13 Apr 2023, Shift 2, 15 Apr 2023, Shift 1, 6 Apr 2024, Shift 1, 7 Apr 2025, Shift 1.

Same topic

Other ideas in Variance and SD

Variance and SD has 20 ideas JEE Main has asked; 10 of them came up in more than one question. The 12 most asked are below.

Topic analysisChapter analysisStudy this chapterAll repeated ideas