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Rounding and estimation
Rounding and estimation

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1 Rounding

1.1 Rounding in daily life

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

‘In your otherwise beautiful poem,’ Babbage wrote, ‘one verse reads,

Every moment dies a man,

Every moment one is born.

‘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:

Every moment dies a man,

Every moment 1 is born

‘Strictly speaking,’ Babbage added, ‘the actual figure is so long I cannot get it into a line, but I believe the figure 1 will be sufficiently accurate for poetry.’

Newspapers, magazines and television often provide numerical information such as that below.

How do you interpret the figures in the headlines above?

It is unlikely that the monthly balance of payments deficit, for example, would be exactly £25 000 000. (Remember 25,000,000 means the same as 25 000 000.) It's more likely to be a number fairly close to £25 000 000: a number like £24 695 481 or £25 332 206. From the reader's point of view, £25 000 000 gives an idea of the size of the deficit; it's a good approximation. Large numbers in particular are often approximated in this way. This process is called rounding.

When you use your calculator, you will need to interpret the results. Part of this interpretation is rounding the answer appropriately.