 # Exam-Style Questions on Significance

## Problems on Significance adapted from questions set in previous Mathematics exams.

### 1.

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, Ho, 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.

### 2.

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, Ho, 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 Ho must be accepted.

### 3.

IB Applications and Interpretation

Ucayali, a multinational technology company that focuses on e-commerce, has a distribution centre in Camelot. As part of a study into healthy lifestyles, the number of cups of coffee drunk by 420 staff members each day were recorded. Results are shown in the table.

Cups of coffee per day

 none 1 or 2 3 or 4 5 or more Office Staff 55 74 82 20 Warehouse Staff 21 33 49 21 Transport Staff 4 21 23 17

The company conducted a $$\chi^2$$ test for independence at a $$5\%$$ level of significance.

(a) State the null hypothesis.

(b) Calculate the p-value for this test.

(c) State, giving a reason, whether the null hypothesis should be accepted.

### 4.

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, Ho, 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.

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.

### 5.

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 ≤ 1616 < S ≤ 20S > 20Total
Female781135328272
Male337815368332
Total11119120696604

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.

### 6.

IB Applications and Interpretation

The Scrumptious Sweet Company sell a variety pack of colourful, shaped sweets. The sweets are produced such that 60% are square and 40% are circular. It is known that 20% of the square shaped sweets and 40% of the circular sweets are coloured red.

(a) Show this information in a tree diagram.

A sweet is selected at random.

(b) Find the probability that the sweet is red.

(c) Given that the sweet is red, find the probability it is circular.

The Scrumptious Sweet Company also produce variety packs of Rainbow Gums. Their specifications state that the colours in each variety pack should be distributed as follows.

 Colour Red Orange Yellow Green Blue Percentage (%) 15 25 15 25 20

Inspector Lou Spowels opens a pack of 90 sweets and records the frequency of each colour:

 Colour Red Orange Yellow Green Blue Observed Frequency 12 21 15 20 22

To investigate if the sample is consistent with the company's specifications, Mr Spowels conducts a $$\chi^2$$ goodness of fit test. The test is carried out at a 5% significance level.

(d) Write down the null hypothesis for this test.

(e) Copy and complete the following table giving the frequencies correct to one decimal place:

 Colour Red Orange Yellow Green Blue Expected Frequency

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

(g) Find the p-value for the test.

(h) State the conclusion of the test. Give a reason for your answer.

### 7.

IB Applications and Interpretation

The 2nd Rutherford American Scouts joined the 37th Wolverhampton British Scouts for an International Camp. Skipper Jones is interested to see if the mean height of American Scouts, $$\mu_1$$, is the same as the mean height of British Scouts, $$\mu_2$$. The information is recorded in the following table.

 American Scout height (cm) British Scout height (cm) 147 153 151 142 155 149 154 156 143 152 149 158 142 146 155 145 149 148 152 143 147 150 149 154 150 144 146

At the 10% level of significance, a t-test was used to compare the means of the two groups. The data is assumed to be normally distributed and the standard deviations are equal between the two groups.

(a) State the null hypothesis.

(b) State the alternative hypothesis.

(c) Calculate the p-value for this test.

(d) State, giving a reason, whether Skipper Jones should accept the null hypothesis.

### 8.

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.

The exam-style questions appearing on this site are based on those set in previous examinations (or sample assessment papers for future examinations) by the major examination boards. The wording, diagrams and figures used in these questions have been changed from the originals so that students can have fresh, relevant problem solving practice even if they have previously worked through the related exam paper.

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