"A difficult exam."
Translation:Un examen difícil.
I have written down a rule... Adjectives fall after nouns, with 'de' in between. e.g. Una hamburguesa de queso
When do you know whether to have the 'de' in between the noun and adjective?
I wrote 'Un examen de dificil' and the correct answer I was given is 'Un examen dificil'
Not an expert but generally it is when it changes the item. For example a red glass is vaso rojo because it is still a glass but a cheese burger is hambergesa de queso because it is a hamburger of cheese.
In Spanish you don't use "de" with adjectives, but with nouns. For example:
Una hamburguesa de queso: queso is a noun, as it is a thing. So you construct the English A cheese hamburguer changing the order and putting de in between.
Una hamburguesa grande: grande is an adjective, so you don't add de to say A big hamburguer.
I 'feel' the difference somehow. I would add to your 'de' rule by saying 'de' is about adjectives for content not for description.
Eg. Un examen de español Un examen difícil
Una tienda de ropa Una tienda elegante