Quantitative Aptitude

Statistics

606 Questions
All Ungrouped data dispersion and consistency 209 Unknown terms from given average 124 Grouped data central tendencies 101 Merging means and variances of groups 53 Replacement change in average 27 Alligation and weighted average 21 Data interpretation from tables and charts 20 Net successive percentage change 19 Grouped data variance via step deviation 18 Combination of multiple ratios 1

Statistics Questions

Multiple choice

In a class there are 40 students and their mean marks are 80. If 20 students who have mean marks equal to 15, leave the class and after that 15 more student who have mean marks 30, admit in the class, find the new mean (approximate).

  1. 95.71

  2. 105.71

  3. 125.52

  4. 150.36

  5. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Initial total marks = 40 * 80 = 3200. After 20 students leave (sum = 20 * 15 = 300), remaining sum = 3200 - 300 = 2900. Remaining students = 20. After 15 students join (sum = 15 * 30 = 450), total sum = 2900 + 450 = 3350. Total students = 20 + 15 = 35. New mean = 3350 / 35 = 95.71.

Multiple choice

The mean and variance of seven observations are 8 and 16, respectively. If 5 of the observations are 2, 4, 10, 12, 14, then the product of the remaining two observations is:

  1. 40

  2. 49

  3. 48

  4. 45
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Mean = (2+4+10+12+14+x+y)/7 = 8 => 42+x+y = 56 => x+y = 14. Variance = 16 = [sum(xi^2)/7] - 8^2 => 80 = sum(xi^2)/7 => sum(xi^2) = 560. 2^2+4^2+10^2+12^2+14^2+x^2+y^2 = 4+16+100+144+196+x^2+y^2 = 460+x^2+y^2 = 560 => x^2+y^2 = 100. (x+y)^2 = x^2+y^2+2xy => 196 = 100+2xy => 2xy = 96 => xy = 48.