A common international convention in business writing is to spell out numbers from one to nine in text and use numerals for 10 upwards. Some style guides switch at 11 rather than 10.
one, two, three
10, 11, 12
Use numerals for percentages and degrees.
10 per cent (or percent for American spelling)
Use commas or spaces to separate large numbers. It’s a style choice whether you use commas in four-digit numbers.
100,000 or 100 000
1000 or 1,000
With currency, use million in text and m or M in tables and brackets.
$10m or $10M
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