Exam-Style Problems

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Nov 2011 p63 q6
3045

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+.

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Nov 2011 p62 q6
3046

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.

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June 2011 p63 q6
3047

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]

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Nov 2010 p62 q6
3048

(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.

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June 2010 p61 q5
3049

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.

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