Learn Icelandic: Er upphæðin mikil?

In Icelandic, mikill (much/great) is the standard adjective for describing a large amount of money (upphæð). While English speakers might say "a high amount" or "a big amount", in Icelandic, an amount is usually described as mikil (great) or lítil (small).

Why is the adjective in the form mikil instead of mikið or mikill?

Adjectives must match the gender of the noun they describe. The noun upphæð (amount) is feminine. Because it is the subject of the sentence, we use the feminine, singular, nominative form of the adjective, which is mikil.

What is the root word for "the amount" here, and how is the "the" added?

The root noun is upphæð (amount). Because it is a feminine word, the definite article suffix used for "the" is -in, which attaches to the end to make upphæðin (the amount).

How does this sentence fit into a lesson about large numbers and thousands?

Upphæð is the specific word used for a monetary amount, bill, or total sum. A typical answer to this question would use the large numbers you are currently practicing, such as Já, hún er tíu þúsund (Yes, it is ten thousand).