# binomial problems/normal problems

• Oct 19th 2010, 05:22 AM
terminator
binomial problems/normal problems
A laboratory supply company breed rats for lab testing. Assume that the male and female rate are equally likely to be born.

What is the probability that 240 of animal born 110 or more will be female?

What is the probability that 240 of animal born 120 or more will be female?
• Oct 20th 2010, 12:46 AM
CaptainBlack
Quote:

Originally Posted by terminator
A laboratory supply company breed rats for lab testing. Assume that the male and female rate are equally likely to be born.

What is the probability that 240 of animal born 110 or more will be female?

The mean number of femails is $120$ and the SD is $\sqrt{240\times 0.5 \times 0.5}=\sqrt{60}\approx 7.75$

So with the normal approximation you assume that the number born $n \sim N(120,60)$ then you want the probablity $P(119.5

CB