Hi !

here are some answers ..

for each qustion, you have two different answer possible. so for the first question 2 possibilities, for the second, 2 possibilities ..2)A physics test contains 25 true/false questions. How many different possible answer keys can be made?

I can't seem to even get started on this 1. The answer is 335,554,43

so you have 2^25 possible answers (=335,554,432)

you have 26 different letters, so 26 possibilities for the first letter, 26 for the second and 26 for the third. you have 10 different digit (0 to 9), so 10 for the first digit, ...3)License plates are to be issued with 3 letters followed by 4 single digits.

a)How many such license plates are possibble? b)If the plates are issued at random, what is the probability that the license place says USA followed by a number that is divisible by 5?

The question doesn't mention if the letters/ digits can be repeated which is whts confusing me. And since it says 4 single digits, they should all be less than 10 right? The right answer is a)175,760,000 b)0.0000114[/COLOR]

26^3 * 10^4 = 175,760,000

b. having a U in the first place have a probability of 1/26, having a S in the second is the same, ..

and whatever the number, you have 2 possibility that it will be divisible by 5 (the last digit should be a 0 or a 5, but not a 1, 2, 3, 4, 6, 7, 8, 9).

so ... (1/26)^3 * (2/10) = 0.0000114

probability of being contractiing the disease:4)A vaccine has a 90% probability of being effective in preventing a certain disease. The probability of getting a disease if a person is not vaccinated is 50%. In a certain geographic region, 25% of the people get vaccinated. If a peron is selected at random, find the probabilty that he/she will contract the disease.

10% is the chance of the vaccine being not effective.

50% chance of getting disease if not vaccinated.

75% in that region are not vaccinated.

75% have a 50% chance of getting it and the 25% have a 10% chance of getting it. So I do 75/50 + 25/10 = 4, but the answer is 0.4.[/COLOR]

1. if the person is vaccined : 1/10

2. if the person is not : 1/2

25/100 of person are vaccined, and 75/100 not,

so .. 25/100 * 1/10 + 75/100 * 1/20 = .4

the three country have 16+15+14 country at all.5)Several territories and colonies today are still under the jurisdiction of another country. France holds the most with 16 countries, the United Kingdom has 15, the United States has 14, and several other countries have territories as well. Choose 3 territories at random form those held by France, the United Kingdom, and the United States. What is the probability that all 3 belong to the same country?

I can't start on this one aswell :'(. The correct answer is 0.097[/COLOR]

you have 16 chance on 45 of helding a french country at first. If its the case, you have then 15 chance on 44 of helding a french country a second time, and 14 out of 43 the third time ...

and so on for the other country,

so.. (16/45 * 15/ 44 * 14/ 43) + (15/45 * 14/44 * 13 / 43) + (14/45 * 13/44 * 12 / 43) = 0.097

Hope it helps ..!