# statistics , question 5, grade 10

5)

- After a survey done on the ages of 50 children on their first day at a scouts’ camp, the results were shown in the following table:

Ages | 7 | 9 | 10 | 12 | Total |

n^{0}” of chidren |
10 | 15 | 20 | 5 | 50 |

- Calculate the mean
and the standard deviation σ.

- Find the number of children whose ages belong to the set:

[

- σ,

+σ ]U{12}.

- That day, a competition was held and only children whose ages are at least 10 can participate, find the percentage of those who can participate.
- On the second day, a group of 12 years old children joined the camp and the mean age becomes 11, find the number of these children.