Answer:
Well that means between the ages of 40 and 60 Bill lost 10 teeth
Step-by-step explanation:
If Bill had 30 teeth when he was 40, and had 20 teeth when he was 60 that means between the ages of 40 and 60 he lost 10 teeth.
Being that 60 minus 40 (60-40=20) is 20, that means he lost 10 teeth in 20 years. Averaging out to loosing 1 tooth every 2 years.
Sorry I was not completely sure what the question was, so I answered it in the most mathematical way possible. Hope I helped a little :)
