PROBABILITY PROBLEM (from newbie)

[cs1x]

I have the follwing question from my exam revision sheets:

"the lengths of a species of worm are normally distributed with a mean length of 21cm and a standard distribution of 1.5cm. find the probability that a worm selected at random is :

1. less than 23.4cm
2. more than 19.8cm
3. between 18-24cm"

since I do not know the total number of worms or the frequency of each worm length I cannot understand how to work this out apart from making the figures up then calculate it out.

any advice would be great, thanks

[Talithin]

tip: revise normal distribution

[cs1x]

tip: revise normal distribution

Thanks Talithin, Managed to suss this one out after posting this thread , Initially I could not understand how to work out the odds without knowing the total number of possible outcomes (like pulling the ace of spades out of a deck of cards).