✔ Class mark is average of lower and upper limits.
Q2. What is the numerator in mean formula?
✔ Numerator is sum of products of frequency and class mark.
Q3. What was the calculated mean in example?
✔ 550 divided by 30 equals approximately 18.33.
Show transcript
[Slide 1] Understanding Grouped Data Mean
When data is grouped, we cannot find exact values. We assume all values lie at the class mark. This helps calculate an approximate average.
[Slide 2] The Direct Method Formula
Use the direct method formula for grouped data. Multiply each class mark by its frequency. Then divide the sum by total frequencies.
[Slide 3] Worked Example Setup
Let us solve a problem with three class intervals. First, calculate the class mark for each interval. Then list the corresponding frequencies in a table.
[Slide 4] Calculating the Mean Value
Multiply class marks by frequencies and sum them up. The total sum is five hundred fifty. Divide this by the total frequency of thirty.
[Slide 5] Avoid Common Calculation Errors
Students often forget to find the class mark first. Another error is multiplying frequencies incorrectly. Always double-check your sums before division.
[Slide 6] Key Takeaways Recap
Remember to find the midpoint of each interval. Multiply by frequency and sum the products. Finally, divide by total frequency for the mean.