High percentage of ice cream (6-4)

I believe the answer is:

ninety-nine

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'ice cream' is the definition.
'ninety-nine' can be an answer for 'ice' (type of ice cream). I'm not certain of the 'cream' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

I've seen this clue in The Independent.

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