More background info:
The given success rates are not that for just the next day, they rather are generic properties of the strategies.
Ie. strategy #1 is correct in about 60% of the prediction cases, strategy #2 is correct in about 10% of the prediction cases.
These values were found by doing countless trials in simulations, or by backtesting historical data.
Each strategy analyses all available data and predicts whether the market (or just a single stock) will close the next day up or down relative to today's close.
For the sake of simplicity let's assume the stock can never close at the same price like yesterday, so there are only 2 possibilities to predict: up or down.