Mean, Median, Mode Questions
Statistics is a vital branch of mathematics that deals with the collection, analysis, interpretation, and presentation of data. Among the most fundamental concepts in statistics are mean, median, and mode. These measures of central tendency help summarize large sets of data into a single representative value.
1.0What is Mean?
The mean, often called the average, is a measure of central tendency used in statistics. It represents the typical value in a set of numbers and gives an overall idea of the data's distribution.
Formula for Mean (Ungrouped Data):
When data is not grouped into classes, it's called ungrouped.
We use the basic average formula:
Mean=Number of observationsSum of all observations=n∑xi
Where:
- xi represents each data point
- n is the total number of data points
Formula for Mean (Grouped Data):
When data is grouped in class intervals, we can't use the simple average.
We calculate class marks (midpoints) first:
xi=2Lower limit + Upper limit
Then use this formula:
xˉ=∑fi∑fixi
Where:
- fi = frequency of class
- xi = class mark
2.0What is the Median?
The median is the middle value of a data set when the numbers are arranged in ascending or descending order. It divides the data into two equal halves and is especially useful when the data set contains outliers.
Formula for Median (Ungrouped Data):
- If the number of observations (n) is odd:
Median=Value at position 2n+1
Median=Average of values at positions 2n and 2n+1
Formula for Median (Grouped Data):
Median=L+(f2N−F)⋅h
Where:
- L = lower boundary of the median class
- N = total frequency (∑fi)
- F = cumulative frequency before the median class
- f = frequency of the median class
- h = class width (class size)
3.0What is Mode?
The mode is the value that appears most frequently in a data set. It represents the most common or popular item.
- If one number appears more than others, it's the mode.
- If two or more numbers appear with the same highest frequency, the data can be bimodal or multimodal.
- If no number repeats, the data has no mode.
How to Find the Mode(Ungrouped Data):
- Look at the list of numbers.
- Count how many times each number appears.
- The number that appears most often is the mode.
Formula of Mode (Grouped Data):
Mode=L+(2f1−f0−f2f1−f0)⋅h
Where:
- L = Lower boundary of the modal class
- f1 = Frequency of the modal class
- f0 = Frequency of the class preceding the modal class
- f2 = Frequency of the class succeeding the modal class
- h = Class width (class size)
4.0Solved Examples on Mean, Median and Mode
Mean, Median, Mode Questions for Competitive Exams
Example 1: The mean of 6 numbers is 12. If one number is removed, the new mean becomes 11. Find the number removed.
Solution:
Let sum of 6 numbers = 6 × 12 = 72
New sum (5 numbers) = 5 × 11 = 55
Number removed = 72 – 55 = 17
Example 2: The median of the data: 7, 9, 4, 5, x, 12, 15 is 9. Find x.
Solution:
Arrange: 4, 5, 7, x, 9, 12, 15
Since median is 9, x must be in correct position so that 4th term is 9:
So, x = 9
Example 3: The mode of the following frequency distribution is 30. Find the missing frequency x.
Solution (Step Sketch):
Mode class = 30–40
Use Mode formula for grouped data:
Mode=L+(2f1−f0−f2f1−f0)⋅h
Where:
- L = 30,
- f1 = 20,
- f0 = x,
- f2 = 10,
- h = 10
30=30+(2(20)−x−1020−x)⋅10⇒0=30−x20−x⇒20−x=0⇒x=20
Example 4: The average of 10 numbers is 20. If 5 of them have an average of 15, what is the average of the remaining 5?
Answer:
Total sum = 10 × 20 = 200
Sum of first 5 = 5 × 15 = 75
Sum of remaining 5 = 200 – 75 = 125
Average=5125=25
Example 5: Find the median of the following data:
Answer:
Cumulative frequency: 3, 8, 15, 19, 20
Total frequency = 20 ⇒ Median position = 10.5th term
Falls in class 30 ⇒ Median = 30
Example 6: If the mode of the data set {a, a + 2, a + 4, a + 6, a + 6, a + 6, a + 8} is 26, find a.
Answer:
Mode is the most frequent term = a + 6
Given: a + 6 = 26 ⇒ a = 20
Example 7: A student records the following marks in 5 subjects: 95, 85, 75, 65, and x. If the mean, median, and mode are all equal, find the value of x.
Answer:
Sorted data: 65, 75, 85, 95, x
Let’s assume mode = median = mean = M
- Median = 85 ⇒ M = 85
- Mean = 565+75+85+95+x=85
⇒ 320 + x = 425 ⇒ x = 105
- Mode must also be 85 ⇒ So 85 should appear at least twice
Update data: 65, 75, 85, 85, 95 ⇒ Now it works!
Example 8: Find the mode of the following grouped data:
Answer:
Modal class = 30–40
L=30,f1=25,f0=10,f2=18,h=10
Mode=30+(2⋅25−10−1825−10)⋅10Mode=30+(2215)⋅10Mode=30+6.82Mode=36.82
Example 9: Five observations have mean 10 and variance 8. If three of them are 5, 10, and 15, find the other two.
Hint: Use:
Mean formula: 5∑x=10 Variance formula:5∑x2−(mean)2=8
5.0Practice Questions on Mean, Median and Mode
- The mean of 6 numbers is 50. Five of them are 45, 55, 60, 35, and 50. Find the sixth.
- Find the mean from the following frequency distribution:
3. Mean of:
4. Find the median of class intervals:
6.0Tips to solve problems related to mean median and mode
- Pay attention to frequency tables.
- Be cautious with even vs odd number of terms.
- Mode can be more than one value (bimodal or multimodal data).
7.0Key Formulas
8.0
9.0Related Questions
1. Is it necessary to memorize formulas for grouped data?
Ans: Yes. For JEE, remember:
Mean (Grouped): xˉ=∑fi∑fixiMedian (Grouped):Median=L+(f2N−F)⋅hMode (Grouped): Mode=L+(2f1−f0−f2f1−f0)⋅h
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