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Probability Level 2

If on an average one birth in 80 is case of twins, What is the probability that there will be at least one case of twins in maternity hospital on a day when 20 births occur?

Use a calculator if required.

0.112 0.222 0.795 0.539

Nagesh Gandewar by Nagesh Gandewar , 28, India

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1 solution

P(a given childbirth is a twin birth) = 1 80 \frac{1}{80}

P(It is not so) = 79 80 \frac{79}{80}

Now, note that the probability that there will be atleast 1 case is the complement of the probability that there will be none.

P(all 20 cases are not twins) = ( 79 80 ) 20 (\frac{79}{80})^{20}

P(there is atleast one twin) = 1 − ( 79 80 ) 20 1 - (\frac{79}{80})^{20}

Now evaluating that will give you the answer

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