If the social security base in Jiujiang, Jiangxi is 20,100, the amount deducted from an individual mainly depends on the contribution ratios of different social insurance types. In general, for an employee, with a social security base of 20,100, the approximate monthly individual deduction is around 2,211 - 2,412 yuan. Here's a breakdown by each type of social insurance:

1. Pension Insurance: The individual contribution ratio is 8%. So the amount deducted for pension insurance is ​
   ×8%=
   yuan. Pension insurance is crucial as it ensures a certain financial support for individuals after retirement.

2. Medical Insurance: The individual contribution ratio is 2%. Thus, the deduction for medical insurance is ​
   ×2%=
   yuan. This helps individuals cover medical expenses when they get sick.

3. Unemployment Insurance: The individual contribution ratio ranges from 0.2% - 1%. Taking the median value of 0.5% for example, the amount deducted is ​
   ×0.5%=100.5
   yuan. Unemployment insurance provides temporary financial assistance when individuals lose their jobs involuntarily.

4. Work - related Injury Insurance and Maternity Insurance: Employees generally do not need to contribute to these two types of insurance. Work - related injury insurance is to compensate employees for work - related injuries, and maternity insurance is mainly for female employees during childbirth - related periods.

It should be noted that the above data is calculated based on common contribution ratios, and actual situations may vary slightly according to local policies and regulations. It is recommended to consult the local social security department for the most accurate information.