Human blood groups are identified by two parts. The first part is A, B, AB or O and the second part (the Rhesus part) is + or −. In the UK, 35% of the population are group A+, 8% are B+, 3% are AB+, 37% are O+, 7% are A−, 2% are B−, 1% are AB− and 7% are O−.
A random sample of 9 people in the UK who are Rhesus + is taken. Find the probability that fewer than 3 are group O+.
There are a large number of students in Luttley College. 60% of the students are boys. Students can choose exactly one of Games, Drama or Music on Friday afternoons. It is found that 75% of the boys choose Games, 10% of the boys choose Drama and the remainder of the boys choose Music. Of the girls, 30% choose Games, 55% choose Drama and the remainder choose Music.
(i) 6 boys are chosen at random. Find the probability that fewer than 3 of them choose Music.
(ii) 5 Drama students are chosen at random. Find the probability that at least 1 of them is a boy.
The probability that Sue completes a Sudoku puzzle correctly is 0.75. Sue attempts 14 Sudoku puzzles every month. The number that she completes successfully is denoted by \(X\).
(ii) Find the value of \(X\) that has the highest probability. You may assume that this value is one of the two values closest to the mean of \(X\). [3]
(iii) Find the probability that in exactly 3 of the next 5 months Sue completes more than 11 Sudoku puzzles correctly. [5]
(i) State three conditions that must be satisfied for a situation to be modelled by a binomial distribution.
On any day, there is a probability of 0.3 that Julie’s train is late.
(ii) Nine days are chosen at random. Find the probability that Julie’s train is late on more than 7 days or fewer than 2 days.
In the holidays Martin spends 25% of the day playing computer games. Martin’s friend phones him once a day at a randomly chosen time.
Find the probability that, in one holiday period of 8 days, there are exactly 2 days on which Martin is playing computer games when his friend phones.