Question

Infants are classied as low birthweight if they have a birthweight <2500g. Suppoe

that infants are also classied by length of gestation aws pre-term ( 36 weeks)

and term ( 37). The chances of a pre-term delivery is 11%. The probability of

low birthweight in a pre-term delivery is 95% and that in a term delivery is 10%.

If a randomly selected baby has normal birthweight, what is the probability that

he/she is born in a pre-term delivery?

Answer 1

	Pre-Term	Term	Total
Low bithweight	0.11X0.95=0.1045	0.89X0.10=0.089	0.1935
Normal bithweight	0.11-0.1045=0.0055	0.89-0.089=0.801	0.8065
Total	0.11	1.00-0.11=0.89	1.00

P(Pre-Term/ Normal birthweight) = P(Pre-Term & Normal birthweight)/P(Normal birthweght)

                                               = 0.0055/0.8065 = 0.0068

So,

Answer is:

0.0068