when to use ‘per cent’ and when to use ‘%’?

In formal writing (articles, academic essays), the form per cent is used after a numeral instead of a percentage symbol or %.

So, this is how percentage should be expressed in academic writing:

’10 per cent of the population still lives below the poverty line.’

‘The report shows that 66 per cent of adolescent children of alcoholic parents exhibit behavioral problems.’

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However, when creating tables, the percentage symbol may be used (%).