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A married couple plans to have four children, and they are wondering how many boy they should expect to have. Assume none of the children will be twins or other multiple births. Also assume the probability that a child will be a boy is \(0.50\). Explain why this is a binomial experiment. Check all four required conditions.

Short Answer

Expert verified
The expected number of boys in the family given these conditions is 2.

Step by step solution

01

Fixed Number of Trials

In this case, the fixed number of trials is the four children the couple plans to have. This means that the experiment will be repeated a fixed number of times.
02

Binary Outcomes

Each child born can either be a boy or not a boy (i.e., a girl). These are the only two possibilities and these outcomes are mutually exclusive, meaning one excludes the possibility of the other.
03

Independence

The sex of each child is independent of the sex of the other children. The gender of a future child is not influenced by the genders of previous children.
04

Fixed Probability of Success

The probability of having a boy, labelled as success in this context, is given as 0.50. This probability is the same for each trial (child). This complies with the requirement of a fixed probability of success.
05

Calculating Expectation

The expected value or mean of a binomial distribution is calculated using the formula \(E(x) = np\), where \(n\) is the number of trials and \(p\) is the probability of success. Here, \(E(x) = 4 * 0.50 = 2\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Fixed Number of Trials
In a binomial experiment, having a fixed number of trials is essential. This simply means we plan to repeat the same experiment a certain number of times. Here, the couple plans to have four children, which can be considered as four separate trials.
Each trial corresponds to the birth of a child.
  • The number of trials is predetermined. In this example, it is exactly four.
  • No additional trials will be added after the four children are planned and born.
By clearly setting the number of trials to four, the scenarios this couple is exploring matches the first condition needed for a binomial experiment.
Binary Outcomes
A key characteristic of a binomial experiment is that each trial should result in just one of two possible outcomes. These outcomes need to be mutually exclusive, meaning if one happens, the other cannot. Here, each child born can either be a boy or a girl.
  • These are the only possible outcomes, covering all possibilities.
  • They do not overlap; a child cannot be both a boy and a girl.
In each trial of having a child, the only relevant outcomes are boy or not a boy (girl). This fulfills the second condition for it to be called a binomial experiment.
Independent Trials
For a series of trials to be used in a binomial experiment, each trial must be independent of the others. In this example, this requirement implies that each child's gender does not affect the gender of any other children.
  • The outcome of one trial (having one child) does not impact the outcomes of any other trials.
  • There isn't any influence between the gender of one child and any siblings born after.
The independence of each trial ensures randomness in the experiment, a quintessential feature of binomial experiments.
Fixed Probability of Success
The fixed probability of success criterion in a binomial experiment dictates that each trial should have the same likelihood of resulting in a 'success'. In this scenario, success is defined as having a boy. The probability of having a boy is given as 0.50, which remains constant for each child.
  • The probability is not affected by previous trials.
  • Each trial (birth) consistently retains the 0.50 probability of success.
With the probability staying fixed across all trials, this example satisfies the final condition necessary for a binomial experiment.

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