What are the odds against drawing a card from an ordinary deck of cards and getting a spade?

You mean the odds of drawing a spade from an ordinary deck of cards?

There are 13 spades in a deck of 52 cards.

The odds of drawing a spade then becomes 13/52 = 1/4

There are 4 houses, you have an equal chance of drawing a spade as you do a heart, clubs, etc. So you have a 25% chance of drawing a Spade.