3. In a class of 100 students 75 are boys and 25 are girls. The chance that a boy gets a first class is 0.25 and the probability that a girl first class is 0.21 . find the probability that a student selected at random gets a first class. ( 3 marks )

In a group of people on holiday, it is established that there are: - 10 males under the age of 21 - 8 females under the age of 21 - 5 females aged between 21 and 30 - 7 males over the age of 30 Calculate the probability that, if one person is selected at random from the group this person will be: \( \begin{array}{l}\text { a) A male under the age of } 30 . \\ \text { b) A female. } \\ \text { c) A male over the age of } 21 . \\ \text { d) A person not older than } 21 . \\ \text { e) A male given that this person is over } 30 \text { years. } \\ \text { f) A female or between } 21 \text { and } 30 . \\ \text { g) A male or a female. }\end{array} \)

- выпполнить в тетради задание: Бросают две игральные кости. Событие \( A \) «на первой кости выпала тройка». Событие \( B \) - «на второй кости выпала тройка». Найди вероятность события \( A \cup B \). (Ответ округли до тысячных.)

16. En una caja hay 8 témperas, cada una de un color diferente. ¿De cuántas maneras distintas se pueden escoger 2 de estas 8 témperas?

Michelle puts 7 red marbles and 5 blue marbles into a bag. If two marbles are chosen at random from the bag, one by one, without replacement, find the probability that two blue marbles are chosen. \( \begin{array}{ll}\text { A } \frac{25}{144} & \text { C } \frac{7}{22} \\ \text { B } \frac{49}{144} & \text { D } \frac{5}{33}\end{array} \)

Jim works at an Auto centre and accidentally drops 4 bad spark plugs into a box with 20 good spark plugs. a. If he selects two spark plugs at random from the box without replacement, and the first spark plug selected was a good one, what is the probability that the second spark plug is bad?