maths_arghh234
Junior Member
- Joined
- Nov 8, 2009
- Messages
- 52
hey .. so our teacher gave us a question sheet.. covering everything we've done .. and i've left it till the last minute ......i know ..i know ..my newyears resolution was not to be lazy as well .. so here 's the bits i'm stuck on
1) ...discrete random variables .. the second part of the question .. evaluate E(1/x) .. i know how to do expected value but what does the 1/x mean ??..what do you do differetnly?/
2) two bags contain red balls and blue balls . bag A contains 3 red balls and 2 blue balls . bag B contains 2 red balls and 4 blue balls two fair coins are tossed and bag A is elected if two heads are obtained . otherwise bag B is selected A ball is then chosen at random from the selected bag .
a) find the probability that bag A is selected ...b) find the probability that the chosen ball is red .. c) given that the chosen ball is red find the probability the bag A was the selected bag .......... i understand it abit ... i'm mainly not sure about what method to use i.e like do you use fractions like very basic probability , combinations .. or what ??
3)A youth club has 120 members of whom 45 are girls and 75 are boys . the leader would like to change the evening on which the meet and he decides to seek the views of the members on this proposed change
a) state what is meant by a census in this context
b) on advantage and one disadvantage of using a sample compared with a census
c) he decides to use a stratified sample of 24 members . the 2 strata being the girls and boys who are members of the club determine the numbers of girls and boys in the sample.. honestly i can't remember anything on sampling i haven't done it this year .. help would be much appreciated !!! thank
1) ...discrete random variables .. the second part of the question .. evaluate E(1/x) .. i know how to do expected value but what does the 1/x mean ??..what do you do differetnly?/
2) two bags contain red balls and blue balls . bag A contains 3 red balls and 2 blue balls . bag B contains 2 red balls and 4 blue balls two fair coins are tossed and bag A is elected if two heads are obtained . otherwise bag B is selected A ball is then chosen at random from the selected bag .
a) find the probability that bag A is selected ...b) find the probability that the chosen ball is red .. c) given that the chosen ball is red find the probability the bag A was the selected bag .......... i understand it abit ... i'm mainly not sure about what method to use i.e like do you use fractions like very basic probability , combinations .. or what ??
3)A youth club has 120 members of whom 45 are girls and 75 are boys . the leader would like to change the evening on which the meet and he decides to seek the views of the members on this proposed change
a) state what is meant by a census in this context
b) on advantage and one disadvantage of using a sample compared with a census
c) he decides to use a stratified sample of 24 members . the 2 strata being the girls and boys who are members of the club determine the numbers of girls and boys in the sample.. honestly i can't remember anything on sampling i haven't done it this year .. help would be much appreciated !!! thank