JEE MATHEMATICS MCQ: STATISTICS

1 Easy

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Application +4 | -1

The mean income of a group of persons is

₹ 400

. Another group of persons has mean income

₹ 480.

If the mean income of all the persons in the two groups together is

₹ 430

, then ratio of the number of persons in the groups is

View answer and explanation

Correct option: A

\frac{n_1}{n_2}=\frac{5}{3}

Option A (n1/n2 = 5/3) is correct because it is derived by setting up a weighted average equation for the combined mean income and solving for the ratio of the number of persons in each group.

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If the mean of a set of observations

{x_1},{x_2}, \ldots ,{x_n}

\bar X,

then the mean of the observations

{x_i} + 2\;i;i = 1,\;2, \ldots ,n

is The sum of 10 items is 12 and sum of their squares is 18 , then standard deviation will be In a family, there are 8 men, 7 women and 5 children whose mean ages separately are respectively 24,20 and 6 years. The mean age of the family is 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

1,3,5, x, y

are 5 observations. Mean of these observations is 5 and variance is 8. Sum of the cubes of the two missing number equals: If s.d. of a set of observations is 8 and if each observation is divided by

-2,

the s.d. of the new set of observations will be