Roll it and count
Experimental probability
Count the fours
You cannot tell how often a die shows 4 just by looking at it. But you can roll it many times and count.
If you roll a die 50 times, how often do you think a 4 will show up?
What this lesson covers
The idea
Experimental probability, the relative frequency of an event, is the number of times the event occurred ÷ the total number of trials, using evidence from repeated trials or past statistical data.
Count the fours
You cannot tell how often a die shows 4 just by looking at it. But you can roll it many times and count.
If you roll a die 50 times, how often do you think a 4 will show up?
- About 8 times
- About 25 times
- Never
Roll the die
Roll the die at least 50 times. The toy tells you how many were fours and the fraction fours ÷ rolls.
Data decides
Experimental probability = number of times the event happened ÷ total number of trials. It is also called the relative frequency.
Roll a die 50 times and get a 4 exactly 8 times. Experimental probability of a 4 = 8/50 = 0.16 or 16%. It comes from real data, not from a guess.
Notes
Experimental probability (relative frequency) = number of times the event occurred ÷ total number of trials. It uses evidence from repeated trials or past data.
Check yourself
A die is rolled 50 times and a 4 shows 8 times. What is the experimental probability of a 4, as a decimal?
Answer: 0.16
8 ÷ 50 = 0.16.
A coin is tossed 40 times and shows heads 18 times. What is the experimental probability of heads, as a decimal?
Answer: 0.45
18 ÷ 40 = 0.45.
In a class of 50 students, 20 like mango. What is the experimental probability that a student chosen at random likes mango?
Answer: 0.4
20 ÷ 50 = 0.4, or 40%.
Experimental probability uses…
- Evidence from repeated trials or past data — correct. Yes. It is based on what actually happened.
- Only the number of faces of the die. That is how theoretical probability works.
- Only an opinion. That would be a subjective probability.