Given that 3rd Quartile (Q3) = 60 . The classes are :

Question

0-10,10-20,20-30,30-40,40-50,50-60,60-7...
70-80,80-90

Now, IN which class does Q3 lie??
50-60 or 60-70?

Answer 1

There is no universal agreement on this. 60, the 3rd quartile, is halfway between the median and the highest data value, usually. See this:
https://en.wikipedia.org/wiki/Quartile