Twelve Batteries were tested to see how many hours they would last.The frequency distribution is shown here.

Twelve Batteries were tested to see how many hours they would last. The frequency distribution is shown here.

Hours             Frequency

1 - 3                    1

4 - 6                    4

7 - 9                    5

10 - 12                1

13 - 15                1

find mean and modal class