What is your exam number?
You have 30 minutes to memorize a series of numbers.
I’m really disappointed right now because she gave me a fake phone number.
A number in a series plus a number. You know what happens when two kanji with basically the same meaning get combined into one by now, right? It just turns out to be the same meaning, basically. This word means number.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.