Step by step
The question
Question: A coin is flipped 20 times and lands tails 9 times.
Find the experimental probability of tails.
1 Times it happened over times tried
It happened 9 times out of 20 flips.
So the experimental probability is 9/20.
P(tails) = 920
Experimental probability comes from what really happened in the experiment.
experimental = what really happened
As a percent: 20 times 5 is 100.
9 times 5 is 45.
So it is 45%.
= 9 × 520 × 5 = 45100 = 45%
2 Compare with the theory
In theory, a coin has 2 sides, so tails is 1 out of 2: 50%.
= theory: 12 = 50%
Careful!
That is the theory.
The question asks what really happened: 45%.
Careful: not P(tails) = 50% ✗
45% is close to 50%.
With more flips, it usually gets even closer.
= 45% < 50%
3 Check
Let's check: 45% of 20 flips should be the 9 times.
45% of 20 is 9.
So the answer is right!
45% of 20 = 9
Let's look back.
First: times it happened over times tried.
Then: compare with the theory.
Last: check.
Answer
= 9 × 520 × 5 = 45100 = 45%