This is a difficult Starter so there is a prize of a watch if you can complete it.
For each pair of numbers multiply the sum by the difference then divide the answer by 5 without using a calculator.
3, 2 
23, 22 
14, 12 
14, 12 
18, 16 
26, 19 
16.5, 16 
11.5, 11.5 
At least one of your answers is wrong.
Congratulations, all of the answers are correct.
You have won a watch. You can watch this sheep for as long as you want!
A Starter which is similar to this one but slightly harder is Multiply, Add, Subtract and Divide.
Topics: Starter  Mental Methods
In any real situation I can think of, if you were to ask someone for the difference between, say, 3 and 5, the answer would be 2 not 2! We tend to think of differences as positive numbers, and thus the proper rendition of that expression algebraically would be 35 (or 53). This is the same idea as the "distance" between two numbers on the number line, which is always positive.
In textbooks, as you've observed, it seems common in 'word problems' to make a different convention, that 'the difference between a and b' means a  b.
The full discussion can be seen here.
Perhaps we'll wait for a few more comments on this page and then adapt this starter to conform with the opinions of the majority. In the meantime you'll see that all the pairs of numbers above have the largest first to take out the ambiguity.
Thanks once again for your feedback 7 Mandelbrot and Laura.How did you use this starter? Can you suggest
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Dividing by five is a great deal to ask,
But an easier method will help you.
Dividing by ten is a much easier task,
Then multiply your answer by two!
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Numbers and the Making of UsI initially heard this book described on the Grammar Girl podcast and immediately went to find out more about it. I now have it on my Christmas present wish list and am looking forward to receiving a copy (hint!). "Caleb Everett provides a fascinating account of the development of human numeracy, from innate abilities to the complexities of agricultural and trading societies, all viewed against the general background of human cultural evolution. He successfully draws together insights from linguistics, cognitive psychology, anthropology, and archaeology in a way that is accessible to the general reader as well as to specialists." more... 
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