Track quiz
Fourteen questions, one idea each. Keep the table beside you.
| Move | How it goes |
|---|---|
| Tally | Classes with no gaps. A boundary reading goes up. |
| Class mark | Add the bounds, then halve. |
| Direct mean | Σ f x ÷ Σ f. |
| Assumed mean | a + Σ f d ÷ Σ f. |
| Step deviation | a + h × Σ f u ÷ Σ f. |
| Median | Count to n ÷ 2, then l + ((n ÷ 2 − cf) ÷ f) × h. |
| Mode | l + ((f₁ − f₀) ÷ (2f₁ − f₀ − f₂)) × h. |
| Choose | A few huge values pull the mean up far more than the median. |
| Missing frequency | Write the mean with f in it. Set it equal to the given mean. Solve for f. |
| Two missing | Use the total to link x and y. Use the median to find x. Then find y. |
| Close the gaps | Half the gap goes to each side. Lower limits go down. Upper limits go up. |
| Below tables | Each class holds its own total minus the total before it. |
A reading of 30 sits on the boundary of 20-30 and 30-40. Which class gets it?
What is the class mark of the class 65-85?
Classes 10-20 and 20-30 have frequencies 8 and 12. What is the mean?
With a = 25, the f × d column adds to −120. There are 30 readings. What is the mean?
Take a = 25 and h = 10. The f × u column adds to −12. There are 30 readings. What is the mean?
The classes are 5-15, 15-25, 25-35 and 35-45. Their frequencies are 4, 9, 12 and 5. Which is the median class?
The median class is 30-40. Here n = 40, cf = 16 and f = 10. What is the median?
The modal class is 30-40. Here f₁ = 15, f₀ = 11 and f₂ = 9. Also h = 10. What is the mode?
On a rainy day most students play a little. A few play very long. Which average shows a typical student?
A table lists frequencies 8, 5, 4 and 3. The list it came from has 21 readings. What does this show?
The frequencies are 3, 5, f and 4. The class marks are 10, 20, 30 and 40. The mean is 25. What is f?
The total is 38. The frequencies are 3, x, 9, 5 and y. What is x + y?
Classes 21-30 and 31-40 leave a gap of 1. What is the second class after the gap is closed?
Below 40: 12 readings. Below 50: 30 readings. How many are in the class 40-50?
This is Chapter 13, Statistics, in your Class 10 book. Try its exercises next.
Next: Probability. It counts what could happen.