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In Roasting Old Chestnuts 3 ,I promised a final look back on school days and some of the mathematics attempted by many school children in preparation for their 'O' level (GCSE).

If Durell was not the arithmetic book that regularly journeyed between home and school then Hall and Stevens could well have been the book you used for this aspect of your mathematical development. Five hundred and odd pages of close type with very few diagrams, the assumption about your level of comprehension and general knowledge was high.

Profit and loss was a rich source of questioning:

- A sells an article to B at a profit of 4 per cent; B sells it to C at a profit of 5 per cent. If C pays £4. 11s. what was the prime cost to A?
[In those days there were 12 pennies(d) to a shilling(s) and 20 shillings to the pound!]

- The total rise in the price of goods passing through three hands is 57
^{1}/_{2}per cent; if the first and second secure profits of 20 p.c. and 25 p.c. respectively, what profit per cent does the third make?[It is not 12

^{1}/_{2}!]Perhaps more in keeping with present times the questions concerned with simple or compound interest and discount would still have some relevance?

- Find, to the nearest penny, the simple interest on £1208. 7s. 10d at 4 per cent, from April 5th to August 10th.
- I borrow £350 on May 1st and a further sum of £270 on August 1st on the understanding that I repay the whole with interst at 3¾ per cent at the end of the year. How much do I owe on December 31st?
Perhaps knowing that:

present value + interest on the present value = sum due

interest on the present value = discount on sum due

will help you with: - What rate per cent. does a man get for his money when in discounting a bill due in 10 months he deducts as discount 4% of the amount of the bill?
Finally while in this fiscal vein:

- A man borrows £200 at 5% compound interest. At the end of each year he pays back £50. How much does he owe at the end of 4 years?

The previous articles in the series were Roasting Old Chestnuts , More Old Chestnuts and Roasting Old Chesnuts III .