Mean

Mean or average or arithmetic mean is one of the representative values of data. We can find the mean of observations by dividing the sum of all the observations by the total number of observations.

Mean of raw data:

If x1, x2, x3, ……. xn are n observations, then

Arithmetic Mean = (x1, x2, x3, ……. xn)/n

= (∑xi)/n

∑ (Sigma) is a Greek letter showing summation


1. Weights of 6 boys in a group are 63, 57, 39, 41, 45, 45. Find the mean weight.

Solution:

Number of observations = 6

Sum of all the observations = 63 + 57 + 39 + 41 + 45 + 45 = 290

Therefore, arithmetic mean = 290/6 = 48.3


Mean of tabulated data:

If x1, x2, x3, x4, ……. xn are n observations, and f1, f2, f3, f4, ……. fn represent frequency of n observations.

Then mean of the tabulated data is given by

= (f1 x1 + f2 x2 + f3 x3 + ……. fn xn)/(f1 + f2 + f3 + …… fn) = ∑(fixi)/∑fi


2. A die is thrown 20 times and the following scores were recorded 6, 3, 2, 4, 5, 5, 6, 1, 3, 3, 5, 6, 6, 1, 3, 3, 5, 6, 6, 2.

Prepare the frequency table of scores on the upper face of the die and find the mean score.

Solution:

Number on the upper
face of die
Number of times it occurs
(frequency)
fixi
1 2 1 × 2 = 2
2 2 2 × 2 = 4
3 5 3 × 5 = 15
4 1 4 × 1 = 4
5 4 5 × 4 = 20
6 6 6 × 6 = 36


Therefore, mean of the data   = ∑(fixi)/∑fi

                                        = (2 + 4 + 15 + 4 + 20 + 36)/20

                                        = 81/20

                                        = 4.05



3. If the mean of the following distribution is 9, find the value of p.

X 4 6 p + 7 10 15
f 5 10 10 7 8


Solution:

Calculation of mean

xi fi xifi
4 5 20
6 10 60
p + 7 10 10(p + 7)
10 7 70
15 8 120


∑fi = 5 + 10 + 10 + 7 + 8 = 40

∑ fixi = 270 + 10(p + 7)

Mean = ∑(fixi)/∑fi

9 = {270 + 10(p + 7)}/40

⇒ 270 + 10p + 70 = 9 × 40

⇒ 340 +10p = 360

⇒ 10p = 360 - 340

⇒ 10p = 20

⇒ p = 20/10

⇒ p = 2



Mean of grouped data:

While calculating the mean of the grouped data, the values x1, x2, x3, ……. xn are taken as the mid-values or the class marks of various class intervals. If the frequency distribution is inclusive, then it should be first converted to exclusive distribution.


4. The following table shows the number of plants in 20 houses in a group

Number of Plants 0 - 2 2 - 4 4 - 6 6 - 8 8 - 10 10 - 12 12 - 14
Number of Houses 1 2 2 4 6 2 3

Find the mean number of plans per house

Solution:

We have
   
Number of Plant Number of Houses
(fi)
Class Mark
(xi)
fixi
0 - 2 1 1 1 × 1 = 1
2 - 4 2 3 2 × 3 = 6
4 - 6 2 5 2 × 5 = 10
6 - 8 4 7 4 × 7 = 28
8 - 10 6 9 6 × 9 = 54
10 - 12 2 11 2 × 11 = 22
12 -14 3 13 3 × 13 = 39


∑fi = 1 + 2 + 2 + 4 + 6 + 2 + 3 = 20

∑fi xi =1 + 6 + 10 + 28 + 54 + 22 + 39 = 160

Therefore, mean = ∑(fixi)/ ∑fi = 160/20 = 8 plants

Statistics













From Mean to HOME PAGE




Didn't find what you were looking for? Or want to know more information about Math Only Math. Use this Google Search to find what you need.



New! Comments

Have your say about what you just read! Leave me a comment in the box below. Ask a Question or Answer a Question.




Share this page: What’s this?

Recent Articles

  1. Counting Numbers from 1 to 50 | Match the Number | Missing Numbers

    Apr 04, 25 03:46 PM

    Math Coloring Pages on Counting Number Oredr
    In counting numbers from 1 to 50, recognize the numbers, count and then join the numbers in the correct number order. Here we mainly need eye-hand coordination to draw the picture and maintain the num

    Read More

  2. Counting Eleven to Twenty with Numbers and Words |Numbers from 11 - 20

    Apr 04, 25 03:21 PM

    Counting eleven to twenty with numbers and words are explained below. One ten and one more is eleven. Eleven comes after ten. One ten and two more is twelve. Twelve comes after eleven.

    Read More

  3. 5th Grade BODMAS Rule Worksheet | PEMDAS | Order of operations|Answers

    Apr 03, 25 03:11 PM

    5th Grade BODMAS Rule Worksheet
    In 5th Grade BODMAS Rule Worksheet you will get different types of problems on mathematical expressions involving different operations, mathematical expression with 'brackets' and 'of' and simplifying…

    Read More

  4. Worksheet on Simplification | Simplify Expressions | BODMAS Questions

    Apr 03, 25 02:58 PM

    Worksheet on Simplification
    In worksheet on simplification, the questions are based in order to simplify expressions involving more than one bracket by using the steps of removal of brackets. This exercise sheet

    Read More

  5. Divisible by 2 Video |Test of Divisibility by 2 Trick| Rules| Examples

    Apr 03, 25 10:25 AM

    Divisible by 2
    A number is divisible by 2 if the digit at unit place is either 0 or multiple of 2. So a number is divisible by 2 if digit at its units place is 0, 2, 4, 6 or 8.

    Read More