## Example 7

Imagine a friend is planning a new kitchen in her house. In the kitchen showroom she noticed that the measurements of most of the kitchen units were given in millimetres. One worktop, for instance, is 575 mm deep. What units should she use to measure the large room in the
Author(s): The Open University

The fraction , is the simplest form of all its equivalent fractions, because it cannot be â€˜simplifiedâ€™ further (by dividing top and bottom by the same whole number called a common factor<
Author(s): The Open University

To subtract one number from another without using a calculator you need to know basic subtractions up to 20. This means that you need to know, off by heart, what result you get if you subtract any number up to 10 from any bigger number up to 20. For example you have to remember that 14 minus 6 is 8, or 9 minus 5 is 4, and so on.

If you are confident that you know the basic subtractions up to 20, carry on with the rest of this course. If you are unsure, or would like some practice to he
Author(s): The Open University

Learning outcomes

After studying this course, you should be able to:

• subtract one number from another

• subtract using decimals

• practise your subtraction skills.

Author(s): The Open University

Keep on learning

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## Study another free course

There are more thanÂ 800 coursesÂ on OpenLearnÂ for you to
Author(s): The Open University

3.3 HIV testing in sub-Saharan Africa

## Example 3.2 HIV testing in sub-Saharan Africa

In developed countries, the standard method for testing whether a person is infected with the virus HIV, that causes AIDS, is to carry out a blood test. Provided such a test is carried out long enough after the initial infection occu
Author(s): The Open University

3.1 Health personnel in Thailand

There are practically no new theories or new principles in this section. We shall work through some examples, and you will see how basic techniques and approaches that you have already learned can be combined to allow you to use tabular data efficiently.

## Example 3.1 Health personnel in Thailand

Author(s): The Open University

Acknowledgements

All materials included in this course are derived from content originated at the Open University.

Course image: Kjetil Korslien in Flickr made available under Creative Commons Attribution-NonCommercial 2.0 Licence.

Except for third party materials and otherwise
Author(s): The Open University

5.6.2 Quartiles when the sample size is awkward

For the six ordered data items 1, 3, 3, 6, 7, 7, the lower quartile is given by

In other words, the lower quartile qL is given by the number three-quarters of the way between x (1)=1 and x (2)=
Author(s): The Open University

5.6 Quartiles and the interquartile range

The first alternative measure of dispersion we shall discuss is the interquartile range: this is the difference between summary measures known as the lower and upper quartiles. The quartiles are simple in concept: if the median is regarded as the middle data point, so that it splits the data in half, the quartiles similarly split the data into quarters. This is, of course, an over-simplification. With an even number of data points, the median is defined to be the average of the middle two: de
Author(s): The Open University

5.4 The mode

The USA workforce data in Table 2 were usefully summarised in Figure 6,
Author(s): The Open University

5.2.2 Birth weights of infants with SIRDS

The data in Table 3 are the birth weights (in kg) of 50 infants suffering from severe idiopathic respiratory distress syndrome. There are two groups of infants: those who survived the condition (there were 23 of these) and those who, unfortunately, did not. The data have not been sor
Author(s): The Open University

2.8 Data and questions: summary

In this section you have met some real data sets and briefly considered some of the questions you might ask of them. They will be referred to and investigated in the remaining sections of this course. Some general principles that govern the efficacy and quality of data summaries and displays will be formulated. As you will discover, the main requirements of any good statistical summary/display are that it is informative, easy to construct, visually appealing and readily assimilated by a non-e
Author(s): The Open University

2.7 Surgical removal of tattoos

The final data set in this section is different from the others in that the data are not numerical. So far you have only seen numerical data in the form of measurements or counts. However, there is no reason why data should not be verbal or textual. Table 7 contains clinical data fro
Author(s): The Open University

3.3 Have I given due consideration to units of measurement?

Many mathematical problems include units of measurement. The measurement may be of length, weight, time, temperature or currency. The UK uses both metric and imperial units.

The table below gives the units of length that are in everyday use in the UK, but you may know some others.

MetricAuthor(s): The Open University

When calculating an answer it is important that you give careful consideration to the order of operations used in the calculation. If you are using a mixture of operations remember that certain operations take priority in a calculation. Consider the following, apparently, simple sum.

Â Â Â 1 + 2 Ã— 3 = ?

What answer would you give?

Did you give 7 as your response, or 9?

The correct answer is 7 but can you explain why?

If you have a calculator handy, check that it
Author(s): The Open University

## Activity 19

In a supermarket the bill comes to Â£8.70, and you have discount coupons worth Â£3.50. The assistant says â€˜that will be Â£12.20 pleaseâ€™. Is she right?

### Author(s): The Open UniversityLicense informationRelated contentCopyright Ã‚Â© 2016 The Open University

Once you have done a calculation, with or without the aid of a calculator, it is important that you pause for a moment to check your calculation.

You need to ask yourself some questions.

1. Have I done the right calculation in the right order?

2. Have I given due consideration to units of measurement?

3. Is my answer reasonable?

4. Did I make a rough estimate to act as a check?

Author(s): The Open University

You will probably think to yourself that the coat shown costs about Â£300. Â£290 is considerably closer to Â£300 than it is to Â£200, so Â£300 is a reasonable approximation. In this case, 290 has been rounded up to 300. Similarly, 208 would be rounded down to 200 because it is closer to 200 than it is to 300. Both numbers have been rounded to the nearest hundred pounds.

When rounding to the nearest hundred, anything below fifty rounds down. So 248 rounds to 200. Anything o
Author(s): The Open University

The English mathematician Charles Babbage, father of modern computing, once wrote to Tennyson regarding one of his poems:

â€˜In your otherwise beautiful poem,â€™ Babbage wrote, â€˜one verse reads,

Every moment dies a man,

Every moment one is born.

â€˜If this were true, the population of the world would be at a standstill. In truth, the rate of birth is slightly in excess of that of death. I would suggest:

Author(s): The Open University