Foreign institutional investors (FIIs) were net buyers of Rs 42.70 crore on August 21, Monday according to data released by Sebi today.While FIIs made gross purchases of Rs 997.10 crore, gross sales totalled Rs 954.40 crore.Mutual funds (MFs) were net buyers of Rs 3.45 crore on Monday. MFs made purchases of Rs 298.75 crore and sales of Rs 295.30 crore.