Although it's hard to be definitive in classifying people as right-or left-handed, some studies suggest that about 14% of people are left-handed. Since 0.14 * 0.14 = 0.0196, the Mul-tiplication Rule might suggest that there's about a 2% chance that a brother and a sister are both lefties. What's wrong with that reasoning?

Question

Mathematics

Aaden Lin

1 June, 09:01

Although it's hard to be definitive in classifying people as right-or left-handed, some studies suggest that about 14% of people are left-handed. Since 0.14 * 0.14 = 0.0196, the Mul-tiplication Rule might suggest that there's about a 2% chance that a brother and a sister are both lefties. What's wrong with that reasoning?

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Savage · Answer 1

Multiplication rule is valid if events are independent. There may be a genetic factor making siblings left-handed or right-handed that is not independent. Therefore, the multiplication rule does not apply.

The reasoning is correct if 2 people are chosen randomly; then, the probability of both been lefties is about 2%, but that doesn't take into account if they are siblings or not.