

このクラスには学生が二十人います。
ここで二十分待ってください。
りんごは二十個ありますか。
"にじゅう(二十)" is in the lesson "Big numbers" (Level 4), along with 11 other useful words. LinDuo has 180 topic lessons like this one, 2,379 words in total. Every word has an illustration, a transcription and pronunciation in a female and a male voice. Just 10–15 minutes a day is enough to learn them all. Free, and works offline.