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You will need formal attire for many occasions, including formal halls and matriculation photos. Expect to get dressed up at least twice a month. Suggested formal wear include:
Dress pants/skirts: best to bring at least one or two.
Dress shirts/Nice blouses: instead of wearing a different formal dress for every occasion, bring lots of nice tops to mix and match with your dress pants/skirts.
Tuxedo/Gown: there are frequent enough black-tie events (i.e. events where the dress code requires a tuxedo) throughout the year that it may be in your interest to purchase a cheap tuxedo in the US. At about £30 a pop for a rental tux in Cambridge, it is a good investment to buy one if you'll need to wear one more than, say, three times and it is a lot cheaper by far to buy one in the US than to buy one in the UK. May Ball gowns can be quite similar to prom dresses so if you have a prom dress that you still fit into, you can bring that. You should be able to get away with wearing a knee-length gown if it's fancy enough.
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