Question 890615
Assuming that they split the rent equally, the rent is $1800/6, or $300 each per month.  For 3 months, each person would pay $300 * 3, or $900.
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More than likely, half of those friends will flake out and stick the leaseholder with their share, meaning that the leaseholder will pay $3600 of the $5400 :-(.
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ALWAYS get any contract, especially those made with friends, in writing.