A boy has 20 permanent teeth and 8 temporary teeth. His age is likely to be:
1.9 yrs
2.10 yrs
3.11 yrs
4.12 yrs
sol:
This particular question is WRONG. Let me explain why? 20 permanent and 8 temporary teeth imply a total of 28 teeth. This can ONLY occur when second molars have come. By the time second molars come, there is absolutely no temporary teeth in the mouth. Further, between 6 and 11 years the total number of teeth always remains the same, i.e. 24.
The relative number of temporary and permanent teeth keeps changing.
The formula to calculate permanent teeth is-
No. of Permanent teeth (between 6 & 11 years) is = (Age in years - 5) X 4.
So the number of permanent teeth at various ages are as follows:
6 yr - > 4
7 yr - > 8
8 yr - > 12
9 yr - > 16
10 yr - > 20
11 yr - > 24