## Exam-Style Questions on Significance## Problems on Significance adapted from questions set in previous exams. |

## 1. | IB Studies |

One hundred and sixty students are asked how many portions of fruit or vegetables on average they have per day. The data collected is organized in the following table.

2 or fewer | 3 or 4 | More than 4 | Total | |

Male | 25 | 35 | 25 | 85 |

Female | 22 | 30 | 23 | 75 |

Total | 47 | 65 | 48 | 160 |

A \(\chi ^2\) test is carried out at the 5% level of significance.

(a) Write down the null hypothesis, H_{o}, for this test.

(b) Write down the number of degrees of freedom for this test.

(c) Find the \(\chi ^2_{calc}\) value for this data.

(d) Find the expected number of females that have more than 4 portions per day (correct to the nearest integer).

(e) Decide whether H_{o} must be accepted.

## 2. | IB Studies |

The older students from Glee High School are required to follow a two year IB Mathematics course. Data were gathered from a sample of 242 students regarding their choice of course. The following data were recorded.

Gender | Studies | Standard | Higher | Total |

Male | 35 | 15 | 21 | 71 |

Female | 60 | 30 | 81 | 171 |

Total | 95 | 45 | 102 | 242 |

A \(\chi ^2\) test was carried out at the 5% significance level to analyse the relationship between gender and choice of mathematics course.

(a) Write down the null hypothesis, H_{o}, for this test.

(b) Find the expected value of female students on the Studies course.

(c) Write down the number of degrees of freedom.

(d) Use your graphic display calculator to determine the \(\chi ^2\)_{calc} value.

(e) Determine whether H_{o} should be accepted. Justify your answer.

One student is chosen at random from the 242 students.

(f) Find the probability that this student is male.

(g) Find the probability that the student chosen at random is on the Standard course.

Two students are chosen at random from the 242 students.

(h) Find the probability that both are on the Studies course.

(i) Find the probability that neither are on the Higher course.

## 3. | IB Studies |

The staff of a shop kept records of who bought smart phones during the month of February one year. They looked at the numbers of phones bought by gender and the size of the screens. This information is shown in the table below; S represents the size of the screen in centimetres.

S ≤ 12 | 12 < S ≤ 16 | 16 < S ≤ 20 | S > 20 | Total | |
---|---|---|---|---|---|

Female | 78 | 113 | 53 | 28 | 272 |

Male | 33 | 78 | 153 | 68 | 332 |

Total | 111 | 191 | 206 | 96 | 604 |

The shop manager wants to use this information to predict the probability of selling these sizes of phone screens for the following month.

(a) Use the table to find the probability that a phone will be bought by a female.

(b) Find the probability that a phone with a screen size of 12cm < S ≤ 16cm will be bought.

(c) Find the probability that a phone with a screen size of 12cm < S ≤ 16cm will be bought by a female.

(d) Find the probability that a phone with a screen size greater than 20cm will be bought given that it is bought by a male.

The manager wants to determine whether the screen size is independent of gender so a chi-squared test is performed at the 1% significance level.

(e) Write down the null hypothesis.

(f) Find the expected frequency for females who bought a screen size of 12cm < S ≤ 16cm to the nearest integer.

(g) Write down the number of degrees of freedom.

(h) Write down the \(\chi ^2\) calculated value.

(i) Determine if the null hypothesis should be accepted. Give a reason for your answer.

## 4. | IB Studies |

A group of students were asked how they get to school each day. The results are shown in the following table

Walk | Bicycle | Car | Bus | Total | |

Male | 22 | 36 | 35 | 56 | 149 |

Female | 32 | 46 | 45 | 50 | 173 |

Total | 54 | 82 | 80 | 106 | 322 |

A \(\chi^2\) test was preformed to see if there was a connection between gender and the method of travelling to school.

(a) Write down what the null hypothesis, H_{o}, might have been for this test.

(b) Find the expected frequency for the females who cycle to school.

(c) Find the \(\chi^2\) statistic.

(d) State whether or not the null hypothesis is accepted at a 5% significance level. Give a reason for your answer.

## 5. | IB Studies |

A survey was conducted asking people's opinions on whether mouthwash should be used before or after brushing teeth. The results are shown as follows.

Age below 18 | Age 18 to 30 | Age over 30 | Total | |

Before | 28 | 29 | 33 | 90 |

After | 24 | 21 | 15 | 60 |

Total | 52 | 50 | 48 | 150 |

A \(\chi ^2\) test at the 1% significance level was conducted.

(a) State \(H_0\), the null hypothesis for the test;

(b) State \(H_1\), the alternative hypothesis for the test.

(c) Write down the number of degrees of freedom.

(d) Find the expected frequency of people between the age 18 to 30 who believe that mouthwash should be used before brushing.

(e) Find the \(\chi ^2\) statistic;

(f) Find the associated p-value for the test.

(g) Determine, giving a reason, whether \(H_0\) should be accepted.

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