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If 30% of all twins are identical twins, what percentage of twins has the same gender? I thought: all identical twins have the same gender so it’s at least 30%. And of the non-identical twins it’s about 50%. So 50+30=80%?? Correct me if I’m wrong..?

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  • $\begingroup$ I agree that same sex twins account for about two-thirds. Note that this means that the naive hypothesis that the three possible configurations BB, BG and GG have equal probability gives the right answer! $\endgroup$ Oct 31, 2020 at 16:25

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You stated:

  • 30% of twins are identical
  • 50% of non-identical twins have the same gender

Therefore 70% of twins are non-identical and 50% of those will have the same gender. I'll leave the rest of the calculation to you.

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    $\begingroup$ So: 35+30= 65% of twins have the same gender? $\endgroup$
    – Mett123
    Jan 5, 2018 at 18:47
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    $\begingroup$ @Mett123 Based on the information you gave, that would be correct. $\endgroup$
    – canadianer
    Jan 5, 2018 at 18:51

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