Learn Hardcore Finnish: Tämä viikko on ollut todellinen haaste, koska minulla on monta koetta. - This week has been a real challenge because I have many exams.

Tämä viikko on ollut todellinen haaste
= This week has been a real challenge.
This is the present perfect. It focuses on the whole week up until now, and often implies the situation is still ongoing (the week is not over yet, or its effects are still felt).
Tämä viikko oli todellinen haaste
= This week was a real challenge.
Simple past. The week is clearly over; you’re looking back at it as something completed.
Tämä viikko on todellinen haaste
= This week is a real challenge.
Simple present. You describe the current state, but less strongly as a “from the beginning up to now” experience. It sounds a bit more static, like a general comment about this week.

In everyday speech, "on ollut" is very natural when the week is still in progress and you want to emphasize the whole experience so far.

Why is it "Tämä viikko" and not "Tällä viikolla"?

Both are correct, but they focus on slightly different things:

Tämä viikko on ollut todellinen haaste
Literally: This week has been a real challenge.
The week itself is the subject – you are talking about the week as a period and characterizing it.
Tällä viikolla on ollut todellinen haaste
Literally: There has been a real challenge this week.
Here "tällä viikolla" (this week, adessive case) is a time adverbial, not the subject. The sentence really says:
A real challenge has existed this week.

The original sentence is more natural for the English idea “This week has been a real challenge”, where “this week” is treated as the thing that is challenging.

Why do we say "minulla on" and not "minä olen" for “I have”?

Finnish expresses possession with a special structure:

minulla on X = I have X
Literally: on me (there) is X.

Explanation:

minä = I (nominative)
minulla = on me, “at me” (adessive case of minä)
on = 3rd person singular of olla (to be)

So structurally the sentence is:

(Jollakulla) on (jotakin).
= Someone has something.
= There is something at someone.

So:

Minulla on monta koetta.
Literally: At me there are many exams.
Meaning: I have many exams.

You can’t say "minä olen monta koetta" – that would mean “I am many exams”, which makes no sense.

Why is it "monta koetta" and not "monet kokeet" or just "paljon kokeita"?

All of these can work, but they differ in form and nuance:

monta koetta
- monta = many (quantifier)
- koetta = partitive singular of koe
  Pattern: monta + [partitive singular]
  This is very common and neutral in meaning: many exams.
monet kokeet
- monet = many (pl., adjectival form of moni)
- kokeet = exams (nominative plural)
  This often has a slightly more specific feel, like talking about a known set of exams:
  Monet kokeet tällä viikolla ovat vaikeita – Many (of the) exams this week are difficult.
paljon kokeita
- paljon = a lot (of)
- kokeita = partitive plural of koe
  This means a lot of exams, emphasizing a large quantity, maybe more than you’d like.

In your sentence, "minulla on monta koetta" is the most straightforward and natural way to say “I have many exams.”

Why is "koetta" singular if the meaning is “many exams”? Isn’t it supposed to be plural?

This is a typical Finnish pattern: certain quantifiers require the partitive singular, even when the meaning is clearly plural.

monta koetta
- monta = many
- koetta = partitive singular of koe

Compare:

yksi koe = one exam (nominative singular)
monta koetta = many exams (partitive singular)
kaksi koetta = two exams (also partitive singular)
kokeet = the exams (nominative plural)
kokeita = exams (partitive plural)

So in Finnish, after numerals 2 and up and after monta, you normally use partitive singular, not a plural form:

kaksi kirjaa (partitive singular of kirja)
monta ystävää (partitive singular of ystävä)

It’s just a structural rule of the language; the “many-ness” is carried by monta, not by the noun ending.

Where does the form "koetta" come from? The base word is "koe", so why not "koeta"?

Koe belongs to a noun type where the stem changes before certain endings, similar to huone → huonetta.

For koe:

nominative singular: koe
genitive singular: kokeen
partitive singular: koetta
nominative plural: kokeet
partitive plural: kokeita

So the stem is actually koke- in most forms. For the partitive singular, -tta/-ttä is added to this stem:

koke- + -tta → koetta

You just have to learn this pattern; many -e nouns behave similarly:

huone → huonetta (a room → a room [partitive])
perhe → perhettä (a family → a family [partitive])
koe → koetta (an exam → an exam [partitive])

That’s why it’s monta koetta, not monta koe or monta koeta.

Why is it "todellinen haaste" and not something like "todellista haastetta"?

The form depends mainly on the verb and on whether you’re talking about:

something as a whole (complete) → nominative, or
something partially / not fully defined → partitive

In "Tämä viikko on ollut todellinen haaste":

subject: Tämä viikko (nominative singular)
predicate noun: todellinen haaste (also nominative singular)
verb: on ollut

With olla (to be), Finnish usually uses nominative for a full identification:

Tämä viikko on (ollut) todellinen haaste.
This week (has been) a real challenge.

Using partitive (todellista haastetta) would sound like you mean “some kind of real challenge (to some extent)” rather than fully naming the week as a challenge. In this context, you’re clearly equating the whole week with a full “real challenge”, so nominative is best.

What exactly does "todellinen haaste" mean? Is it the same as “really challenging”?

todellinen haaste literally means “a real challenge”:

todellinen = real, genuine, actual
haaste = challenge

It’s similar in tone to English:

This is a real challenge. (= quite difficult / demanding.)

You could also say:

todella haastava = really challenging (adverb + adjective)
Tämä viikko on ollut todella haastava.
This week has been really challenging.

Nuance:

todellinen haaste feels like a somewhat fixed expression, slightly idiomatic.
todella haastava just describes the week as very challenging, more neutral.

Both are correct; the original just uses the common idiom “a real challenge”.

Why is the conjunction "koska" used here? Could we use "sillä" or "että" instead?

The sentence has a reason clause:

…, koska minulla on monta koetta.
= …, because I have many exams.

Common conjunctions and differences:

koska
= because
Neutral, very common for introducing the reason for something.
sillä
Also often translated “because”, but feels a bit more explanatory / stylistic, and is more common in written, somewhat formal language.
You might see:
Tämä viikko on ollut todellinen haaste, sillä minulla on monta koetta.
This is fine; it sounds slightly more written/formal.
että
= that (introduces a content clause)
Not used here.
Minä tiedän, että sinulla on monta koetta.
I know that you have many exams.

So in your sentence, koska is the most straightforward and natural choice for “because”.

Is the word order "koska minulla on monta koetta" fixed, or can it be changed?

Finnish word order is relatively flexible, but there is a neutral, default order, especially in subordinate clauses like those after koska:

[koska] [subject] [verb] [other parts]
koska minulla on monta koetta

Possible variations:

koska monta koetta minulla on – Grammatically possible, but sounds marked / emphatic, maybe focusing on how many exams.
koska minulla monta koetta on – Also possible but unusual; might appear in some emphatic or poetic contexts.

For normal, everyday speech and writing, "koska minulla on monta koetta" is the natural word order and matches the English “because I have many exams.”