# Thread: probability with teen pregnancy

1. ## probability with teen pregnancy

heres the question.
What is the conditional probability that a teenage pregnancy is in a young mother 15 to 17 years old, given that she is classified as white ? what is the conditional probability that a teenage pregnancy is in a young mother 15 to 17 years old, given that she classified as black.

heres the chart
-----------------15 to 17 -----------------18 to 19
white--------------23------------------------.49
black--------------.09-----------------------.15
other--------------.01-----------------------.03

THANKSS!! any help would be helpful!

2. Originally Posted by gbgb
heres the question.
What is the conditional probability that a teenage pregnancy is in a young mother 15 to 17 years old, given that she is classified as white ? what is the conditional probability that a teenage pregnancy is in a young mother 15 to 17 years old, given that she classified as black.

heres the chart
-----------------15 to 17 -----------------18 to 19
white--------------23------------------------.49
black--------------.09-----------------------.15
other--------------.01-----------------------.03

THANKSS!! any help would be helpful!
Use Bayes' Rule.

For white:

$P(15-17 | W) = \frac{P(W | 15-17)P(15-17)}{P(W | 15-17)P(15-17) + P(W | 18-19)P(18-19)}$

$= \frac{(.23)(.33)}{(.23)(.33) + (.49)(.67)}$

For black:

$P(15-17 | B) = \frac{P(B | 15-17)P(15-17)}{P(B | 15-17)P(15-17) + P(B | 18-19)P(18-19)}$

$= \frac{(.09)(.33)}{(.09)(.33) + (.15)(.67)}$

3. Originally Posted by gbgb
heres the question.
What is the conditional probability that a teenage pregnancy is in a young mother 15 to 17 years old, given that she is classified as white ?
23/(23+49)~=0.319

Explanation: in a sample of 100 teen pregnancies 72 are white, and of those 23 are "15 to 17"'s (on average)

RonL