They just asked me to translate English to Portuguese: "My pants are not red." I typed "Minhas calças não é vermelhas" and they marked it wrong, said it was "Minha calça não é vermelha." But now they've asked me to translate Portuguese to English, and the sentence they gave me was "Minhas calças não são vermelhas." Que??
"My pants are not red" can refer to either one pair of pants or two pairs of pants. Therefore, it can be translated as "Minha calça não é vermelha" (speaking of one pair) or "Minhas calças não são vermelhas".(speaking of two pairs).
Apparently the program detected "é", so it converted your entire sentence to singular when it marked you wrong and corrected you.