What percent decrease occurs when a stock goes from 6.50 per share to 4.25 per share?

This is a 35% decrease.

To find the percent decrease, find the amount of decrease:  6.50 - 4.25 = 2.25.  Now divide this by the original price of the stock:

2.25/6.50 = 0.3462 ≈ 0.35