12. The fo l lowing tab le s h ow s th e annual returns (in percent ) for th e Vanguard Energy Fund from 2 0 0 5 th rou gh 2 009.

Year Energy 2005 44.60 2006 19.68 2007 37.00 2008 − 42.87 2009 38.36 Source: www.finance.yahoo.com.

a. Calculate th e p o in t e s t ima te o f σ .

b. Cons truct a 95% c o n f id en c e interval o f σ .