Though among friends you can just say arigatou and gomen.
Learning to count to 100 in Japanese is super easy. Unlike in English, we only have to remember how to count to ten:
1 - いち (ichi)
2 - に (ni)
3 - さん (san)
4 - よん (yon)
5 - ご (go)
6 - ろく (roku)
7 - なな (nana)
8 - はち (hachi)
9 - きゅう (kyuu)
10 - じゅう (juu)
To count to 11, you just add ten plus one so it's Juu Ichi. 12 is ten plus two, or Juu Ni. As for 20 or 30, you have two tens so Ni Juu or three tens, or San Juu. 47 would then be Yon Juu Nana. You can do this all the way up to 99, with 100 being called 「ひゃく」 hyaku.
To elaborate, though, Japanese numbers change based on what your are counting. This can be very complicated, but today I wanted to let you know how to say how old you are. For this, you simply take your age and add sai desu. This means "--- years old, I am" or "I am --- years old." For this you have to remember three changes. Ichi becomes Is, Hachi becomes Ha and Juu becomes Ju.
