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.

There are four nitrogenous bases that make up dna. the two pyramidines are thymine and cytosine. the two purines are adenine and guanine. these bases pair in a very specific way. adenine - thymineguanine - cytosine i remember it like this: a tall, good cat.

Sorry  i don't understand can you rephrase that