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Class 9 Statistics and Probability for AI: cheat sheet
CBSE Computational Thinking and AI. Statistics sums up data with mean, median, mode and range; probability measures how likely an event is, from 0 to 1.
Key ideas
- The mean shares the total equally; the median is the middle of the sorted data; the mode is the most common value.
- With an even number of values, the median is the average of the two middle ones.
- The range, largest minus smallest, shows how spread out the data is.
- Probability = favourable outcomes ÷ all outcomes, written as a fraction in lowest terms.
- An impossible event has probability 0 and a certain event 1; the chance of “not A” is 1 − P(A).
- AI models use these ideas: averages to sum up data, probability to say how sure a prediction is.
Remember
| Mean | sum ÷ number of values |
| Median of 22, 29, 33, 34, 37, 37 | (33 + 34) ÷ 2 = 33.5 |
| Probability | bag of 3 red, 5 blue, 2 green: P(red) = 3/10, P(not blue) = 5/10 = 1/2 |
| P(A or B), no overlap | P(A) + P(B) |
| Words | 0 impossible; less than 1/2 unlikely; 1/2 equally likely; more than 1/2 likely; 1 certain |
Watch out
- Taking the middle value before sorting the data.
- Leaving a probability as 5/10 instead of 1/2.
- Dividing by the number of colours instead of the number of balls.
Worked example
Find the median of 29, 34, 37, 37, 22, 33.
Working: in order: 22, 29, 33, 34, 37, 37; average of the middle two
Answer: 33.5
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