In a frequency distribution, the mid value of a class is 20.5 and the width of the class is 10. The lower limit and upper limit of the class is

1. 15.5, 25​
2. 15, 25​
3. 15.5, 25.5​
4. 15, 25.5​

In a frequency distribution, the mid value of a class is $10$ and the width of the class is $6$. The lower limit of the class is

In a frequency distribution, the class-width is 4 and the lower limit of first class is 10. If there are six classes, the upper limit of last class is