Aunque el ejercicio parecía difícil, al final pude sumar, restar y encontrar el número exacto sin ayuda.

Aunque means although / even though. It introduces a contrast:

• Aunque el ejercicio parecía difícil = Although the exercise seemed difficult
• al final pude... = in the end I managed to...

So the idea is: something looked hard, but the speaker still succeeded.

A useful note: aunque can be followed by either the indicative or the subjunctive, depending on meaning.

• Aunque parecía difícil → the speaker presents it as a real or accepted fact/perception.
• Aunque parezca difícil → more like even if it seems difficult or although it may seem difficult.

In your sentence, parecía is in the indicative because the speaker is talking about how it actually seemed.

Parecía is the imperfect of parecer. Here it describes a background impression or ongoing appearance:

• parecía difícil = it seemed difficult

The imperfect is very common for descriptions, states, and how things looked or felt in the background of a story.

Compare:

• El ejercicio parecía difícil = The exercise seemed difficult / looked difficult.
• El ejercicio pareció difícil = The exercise seemed difficult at a specific moment.

In this sentence, parecía fits better because the speaker is setting the scene before the result: it looked difficult, but later they managed to do it.

Pude is the preterite of poder and here it means I managed to / I succeeded in being able to.

• pude sumar, restar y encontrar... = I managed to add, subtract, and find...

This is different from podía, which usually means I was able to / I could in a more general or ongoing sense.

Compare:

• Podía hacerlo = I could do it / I was able to do it in general.
• Pude hacerlo = I managed to do it / I succeeded in doing it.

Since the sentence is about a completed result in the end, pude is the natural choice.

Spanish often leaves out subject pronouns because the verb ending already tells you who the subject is.

• pude clearly means I was able / I managed
• so yo is unnecessary

You could say yo pude if you wanted emphasis or contrast, for example:

• Yo pude hacerlo, pero él no. = I managed to do it, but he didn’t.

But in a normal sentence like this, leaving out yo sounds natural.

Al final means in the end / in the end after all / finally.

In this sentence:

• al final pude... = in the end I managed to...

It suggests there may have been difficulty, doubt, or effort before the successful result.

A small nuance:

• al final often emphasizes the outcome after a process
• finalmente can also mean finally, but sometimes sounds a little more formal or simply marks the last event

Here, al final is very natural.

After poder, Spanish normally uses an infinitive.

• pude sumar
• pude restar
• pude encontrar

This works just like English could + verb or managed to + verb.

So the structure is:

• pude + infinitive

Because the speaker is talking about several actions they managed to do, all three verbs stay in the infinitive:

• sumar
• restar
• encontrar

They are math verbs:

• sumar = to add
• restar = to subtract

So:

• pude sumar y restar = I managed to add and subtract

These are standard, everyday words in Spanish for arithmetic.

Also useful:

• la suma = addition / sum
• la resta = subtraction
• sumar dos más dos = to add two plus two
• restar cinco menos tres = to subtract three from five / do five minus three

Because número is a masculine noun in Spanish:

• el número
• not la número

Since adjectives must agree with the noun, exacto is also masculine singular:

• el número exacto

If the noun were feminine, the adjective would change:

• la cifra exacta
• la respuesta exacta

So the agreement here is:

• número → masculine singular
• exacto → masculine singular

Sin ayuda means without help, in a general sense. Spanish often leaves out the article when talking about something in a broad, non-specific way.

• sin ayuda = without help
• sin agua = without water
• sin problemas = without problems

If you say sin la ayuda, it usually means without the help, referring to a specific help that has already been identified:

• sin la ayuda de mi profesor = without my teacher’s help

So in your sentence, sin ayuda is the natural general expression.

The comma separates the subordinate clause introduced by aunque from the main clause.

• Aunque el ejercicio parecía difícil, = subordinate clause
• al final pude sumar, restar y encontrar el número exacto sin ayuda. = main clause

This comma is very natural in Spanish, especially when the sentence begins with a longer introductory clause.

It helps the reader hear the pause and understand the structure clearly.

No. Ejercicio can mean a physical exercise, but it also very commonly means an exercise, task, or problem in schoolwork, maths, grammar, etc.

In this sentence, el ejercicio almost certainly means:

• a maths exercise
• a problem
• a practice task

So here it is not about working out physically. It is more like the exercise/problem seemed difficult.

Yes, depending on context, that can be a very natural translation.

Literally, encontrar el número exacto is to find the exact number. But in English, if this is about a maths problem, native speakers might naturally say:

• find the exact answer
• work out the exact number
• get the exact number

So the most literal translation is find the exact number, but find the exact answer may sound more natural in some contexts.

A natural translation would be:

Although the exercise seemed difficult, in the end I managed to add, subtract, and find the exact number without help.

Other natural versions are also possible, such as:

• Although the problem seemed difficult, I was able to add, subtract, and find the exact number on my own in the end.
• Even though the exercise looked difficult, I eventually managed to add, subtract, and work out the exact number without help.

The best English version depends on context, but the Spanish structure and meaning stay the same.