Given that:
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You know that in order for the number of girls to be significantly high, the probability must be:
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In this case, you can determine that 58 girls in 100 births is a significantly high number, because:
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And:
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Notice that the probability for exactly 58 girls is less than 0.05.
Hence, the answer is:
The relevant probability is
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so 58 girls in 100 births is a significantly high number because the relevant probability is less than 0.05.