First of all, let's define some concepts:
1. Definite articles are used to talk about specific nouns. In Spanish, few nouns can stand alone. In this way, there are four definite articles: el, la, los, and las. Nouns are often accompanied by articles. So the use of them points out the gender (either masculine or feminine) and number (either singular or plural) of a noun. As we said there are four definite articles in Spanish, and they often all translate to the same word in English: the. In the first Table below is shown the four forms that Spanish definite articles take. There are some exceptions to this rule. For example, if a feminine singular noun starts with a stressed a or ha sound then we use the masculine definite article rather than the feminine definite article.
2. Indefinite articles are used to talk about something that is not defined. Spanish indefinite articles, which translate to a, an, some or a few in English match with the nouns they modify in both number and gender. So, we use indefinite articles to indicate the gender (either masculine or feminine) and number (either singular or plural ) of a noun. So in the second Table below is indicated the indefinite article forms. It is important to note that the indefinite article always has to match both the gender and number of its noun. Also, there are some exceptions, for example, if a feminine singular noun starts with a stressed a or ha, the masculine indefinite article un is used rather than the feminine indefinite article una.
3. Descriptive adjectives describe some quality of a noun. In Spanish, adjectives have to agree with the noun or pronoun they describe in both number and gender. What this means is that if a noun an adjective describes is masculine, the adjective must be masculine, and if that same noun is singular, the adjective must be masculine and singular as well. Moreover, there are some rules for matching adjectives to their respective nouns in both gender and number.
3.1. Adjectives Ending in o:
These are the most common adjectives in Spanish. So, adjectives ending in o in the masculine singular form have four possible endings as indicated in the third Table. In this way, if you want to change the masculine singular form of an adjective to match a feminine noun, you need to replace the o ending with an a. On the other hand, if you want to make an o adjective plural in the masculine or feminine form, add an s to the singular ending.
3.2. Adjectives Ending in e or ista:
This type of adjectives does not change with the gender. Therefore, they agree with both feminine and masculine nouns in the singular form, though they do change for number as shown in the third Table.
3.3. Adjectives Ending in a consonant:
In Spanish, most adjectives ending in a consonant don't change with the gender, but do change for number, just like adjectives ending in e. If you want to make plural an adjective ending in a consonant, you need to add es to the singular ending. Moreover, there are some exceptions that we need to take into account, these exceptions are also shown in the third Table:
a) Adjectives ending in z in the singular, change the z to a c before adding the plural ending.
b) Adjectives ending in or, ón, or ín do have feminine forms. You need to add a or as to the masculine singular form and, if necessary, delete the written accent.
c) Adjectives ending in erior do not have a feminine form.
So from these concepts we can solve this problem as follows:
1. Las camisas verdes
2. Los niños simpáticos
3. Una muchacha triste
4. Muchos amigos simpáticos
5. Una casa grande
6. Alguna tarea interesante
7. Los hermanos jóvenes
8. Mucha tarea difícil