"The small village has twenty-eight houses."
Translation:Das kleine Dorf hat achtundzwanzig Häuser.
Because the adjective is in front of a noun (it's an attributive adjective), it has to have an ending -- klein is the only form it cannot be.
Which ending to choose depends on what is in front of it (here: the definite article das, so you need weak inflection) and the gender, number, and case of the following noun (here: neuter nominative singular).
Does the reply given below apply to all adjectives which precede the noun?
The -e ending here is not strong feminine; it's weak nominative singular.
Attributive adjectives (before a noun) inflect differently depending on whether or not there is a determiner before them (such as a definite or indefinite article or a possessive determiner) and if so, what kind -- so they can take strong, weak, or mixed inflection.
Generally, Duo accepts numbers in digits in the base language (here: English) but not in the learning language (here: German).
Because if you write "28 Häuser", that doesn't show that you know how to pronounce "28" in German, so it asks you to write it out in words.
Duo should be consistent.
Isn't it? Consistently accepting "28" in English sentences and consistently rejecting "28" in German sentences?