Now, let's say that Apple releases some incredibly positive news tomorrow, and its shares jump by 20%, or to $113.62. This would raise the price-weighted average to $64.53, a 10.8% jump.

For example, a stock’s 50-day moving average is its mean price over the last 50 days, while its 200-day moving average is its mean price over the last 200 days. Moving averages come in a few ...