Learn Portuguese (Portugal): Ele chumbou no exame de matemática.

While falhar means to fail at a task or miss a goal, it is not normally used for school grades or tests. In Portugal, chumbar (which comes from chumbo, meaning lead) is the most common everyday word for failing an exam or a school year. You can also use the slightly more formal verb reprovar.

Why does the sentence use no (em + o) before the exam?

In English, you directly "fail an exam", but in Portuguese, the verbs for failing a test (chumbar and reprovar) require the preposition em. You literally say that someone failed in the exam, which combines the preposition em with the masculine article o to make no.

Why is it just de matemática and not da matemática?

When a noun acts as a general category or describes the type of another noun—like naming the subject of an exam—Portuguese usually drops the definite article. You use the simple preposition de because it is a general "maths exam", rather than an exam about one specific, previously defined set of mathematics.

Why is the verb in the Pretérito Perfeito (chumbou) instead of the Imperfeito (chumbava)?