No one of us knew the age of Lisa, our math teacher, and the six guesses were as follows:
34,47,48,53,30 and 40.
When confronted with this list , Lisa joyfully said:
I will not disclose my age explicitly, but I let you know that all of you erred.
Your estimates were off by: 2,6,11,12,8,5.

Well, it took some reasoning to get her true age.

What was it?