During a 30 year period a severe drought occurred in three separate years according to this information what is the yearly frequency of drought?

During a 30 year period, the yearly frequency of drought is 10%, which is experienced in three separate years.
Additionally, drought is a period where precipitation is below average and thus resulting in prolonged shortages of water supply as far as both ground and surface water are concerned. This can last for several months or even for years.

Ithink the answer is c. i’m not sure though i’ll notify you when i have an exact answer!