In 2006, Sheri invested $1,000 in the stocks of each of three companies, X, Y, and Z. Over the next four years, as the stock prices changed, the value of her investments changed as follows:

2006 2007 2008 2009

X $1000 $3000 $500 $1000

Y 1000 1000 2000 2000

Z 1000 500 3000 500

a) Set up a table showing the percentage change in the value of each of Sheri's stocks each year over the previous year, and the percentage change in each stock over the four-year period.

b) What was the percentage change in the value of Sheri's total investment, each year, and over four years?