Numerology (not to be confused with Angel numbers!) is a fascinating subject of its own, but in tarot, you can use basic numerology to help understand the meaning of the card.  For example, if you know that the number Eight corresponds with Strength, then you can apply that to the Suit that is drawn to come up with a simple way to remember the cards! Using this example, the Eight of Wands with mean a strong passion, the Eight of Pentacles a strong work ethic, etc.