# Confidence intervals for percentage share of multiple response

If I have a sample of 100, who give responses to a set of multiple response variables, say for example, the brands they have purchased in the last 12 months.

How can I calculate the confidence intervals around the percentage for the share of all purchases for a particular brand?

I can use standard confidence interval formula for CI around "%" but can the same be said for CI around "Share %" as displayed below?

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Brand   |  N   |   %   | Share %
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Brand1  |  20  |  20%  |  9%

Brand2  |  40  |  40%  | 19%

Brand3  |  45  |  45%  | 21%

Brand4  |  35  |  35%  | 16%

Brand5  |  75  |  70%  | 35%
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Total   | 215  |       | 100%
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