Lauren Laverne has just had a mathematician on her show returning for her weekly slot having had a break to have her second child. Her first child was a girl. What are the chances, she asked, that the girl now has a sister?
She made it multiple choice giving 1/2, 1/3 or 13/27 as the possible answers.
According to the maths the answer is 1/3. There are 4 possible sibling combinations, boy/boy, boy/girl, girl/boy, girl/girl. Knowing it can't be boy/boy leaves 3 possible combinations hence a 1 in 3 chance that the older girl now has a baby sister.
Surely this is wrong though. The siblings in each combination aren't equal. One is older than the other. If the first child in each combination is the older child then the possible answers are reduced to girl/boy and girl/girl hence the answer to the question is 1/2.
Who's right?
She made it multiple choice giving 1/2, 1/3 or 13/27 as the possible answers.
According to the maths the answer is 1/3. There are 4 possible sibling combinations, boy/boy, boy/girl, girl/boy, girl/girl. Knowing it can't be boy/boy leaves 3 possible combinations hence a 1 in 3 chance that the older girl now has a baby sister.
Surely this is wrong though. The siblings in each combination aren't equal. One is older than the other. If the first child in each combination is the older child then the possible answers are reduced to girl/boy and girl/girl hence the answer to the question is 1/2.
Who's right?
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