statistics , question 5, grade 10

5)

1. 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
n0” 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.