EXAMPLE 12 Stocks go up, stocks go down

On September 10, 2001, the NASDAQ composite index of stock prices closed at 1695.38. The next day the September 11 terrorist attacks occurred. A year later, on September 9, 2002, the NASDAQ index closed at 1304.60. What percentage decrease was this?

194

That’s a sizable drop. Of course, stock prices go up as well as down. From September 10, 2002, to September 9, 2003, the NASDAQ index rose from 1320.09 to 1873.43. That’s a percentage increase of

Remember to always use the starting value, not the smaller value, in the denominator of your fraction. Also remember that you are interested in the percentage change, not the actual change (here, the 41.9% is the correct value to report instead of the 553.34 difference).