What is the extent of liability when two or more individuals guarantee a debt jointly?

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If two individuals guarantee a debt of one thousand for a person using the phrasing 'We guarantee for you the thousand owed by Zaid,' then each individual is responsible for half the amount. If there are three guarantors, each is responsible for one-third. If one states, 'I and these two guarantee the thousand for you,' and the other two remain silent, only the speaker is liable for one-third of the thousand, and the other two incur no liability.