Historical data shows that the number of goals scored per match at European Football Championships has a mean of 1.93 and a variance of 1.4. A large random sample of n matches is taken. Find the least value of n such that the probability that the average number of goals scored per match exceeds 2 goals is less than 0.24.
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Worked solution
6
1. State the approximate distribution of the sample mean using the Central Limit Theorem.
Let be the number of goals scored per match.
We are given and .
Let be the sample mean number of goals in a sample of size .
Since is large, by the Central Limit Theorem, is approximately normally distributed:
2. Formulate the probability inequality given in the question.
The probability that the average number of goals exceeds 2 is less than 0.24:
3. Standardise the normal variable and equate to the inverse normal value.
Standardising to the standard normal variable :
From standard normal tables or a calculator, the critical value where is .
For the upper tail probability to be strictly less than , the standardised value must be greater than this critical value:
4. Solve the inequality for $n$.
5. State the final integer value for $n$.
Since the sample size must be an integer, the least value of is .
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