Foreign institutional investors (FIIs) were net buyers of Rs 487.10 crore on August 31, Thursday according to data released by Sebi today.While FIIs made gross purchases of Rs 2194.50 crore, gross sales totalled Rs 1707.40 crore.Mutual funds (MFs) were net buyers of Rs 54.45 crore on Thursday. MFs made purchases of Rs 555.03 crore and sales of Rs 500.58 crore.