Question about Statistcs

Question

Assuming that he weights of a newborn babies at a certain hospital are normally distributed with mean 6.5 pounds and standard deviation 1.2 pounds, how many babies in a group of 80 babies from this hospital will wigh more than 8.9 pounds?

Answer 1

cakculate z = (x-mean)/sd = (8.9- 6.5)/1.2 = 2.4/1.2 = 2

by the empirical rule 95% fall within 2 sds of the mean

and (1- .95)/2 = .05/2 = .025 = 2.5% fall more than 2 add to the right of the mean

80 x .025 = 2 babies will weigh more than 8.9 pounds, on average

that's a rough approximation using the empirical rule. For a more accurate number use the z tables or a statistics calculator

if for example, expected value = 2.2 then

(2x2 +3t)/(2+t) = 2.2

4 +3t = 4.4+2.2t

.8t = .4

t = .5

for every four 2's, there's one 3 expected, on average

with z tables:

.028717 x 80= about 2.29736 babies expected to weigh over 8.9 lbs