March 16 on Private Schools

In few places around the world are public schools preferred to private schools even among affluent families. Singapore is one of them. 

In 2013 SIM's enrollment hit a high of 23,000, with 20,000 locals. Last year, the number fell to 21,500, with 18,000 locals. 

What is the percentage decrease of local students in SIM? Can the decrease be expressed as a fraction? State a unit feaction that can be used as a good estimate for the percentage decrease.

The reason is because there are now more places in the public universities. SIM is a private school.