Chance and probability · Usually met around P3
Experiments and their results
Tally in fives; more tries come closer to expected.
How to do it
Method
Tally in fives; more tries come closer to expected
Two fives and 3 marks: 5 + 5 + 3 = 13
Another way
Expected first
4 results, 20 tries: about 5 each
In full
In an experiment, each time you get a result, make a mark in its row of the table, in fives (four upright, the fifth across), and count them in fives. To read the results: the rows added together are how many times you tried; the biggest number is the result that came most often. Results needn't match what you expect exactly: 20 coin tosses should give about 10 heads, but 8 or 12 can happen. The more times you try, the closer each result's share usually gets to what you expect. Or work out the expected numbers first: 4 equally likely results over 20 tries give each about 20 ÷ 4 = 5.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
Chi-keung tossed a coin and recorded the results in the table. How many times did Chi-keung toss it?
Show the answer and working
Answer: 27
Every toss gives one result: 19 heads and 8 tails make 27.
Example 2
May spins a spinner and keeps a tally of the results. How many times did it land on blue 🔵?
Show the answer and working
Answer: 13
Count the blue row's marks: each group of five is 5, plus the marks left over: 13.
Example 3
Tsz-ching took balls from a bag, putting each one back, and recorded the results. Which colour came up most often?
- A. Yellow 🟡
- B. Red 🔴
- C. Blue 🔵
- D. Green 🟢
Choose the right answer
Show the answer and working
Answer: D. Green 🟢
Compare: red 5, blue 10, yellow 11, green 12; the biggest came up most often.
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