I searched this forum regarding these questions but was unable to find them.

Could anyone PLEASE help me to solve these problems??

#37: The numbers (1,2,3,6) have an average (arithmetic mean) of 3 and a variance of 3.5. What is the average (arithmetic mean) and variance of the set of numbers (3,6,9,18)

answer is 9, 31.5

How do you find variance?

Isn't it

S^2= sum (x-average)^2 / n-1 ?

I don't know how to get 31.5!

#38. Jill has 6 different books. in how many ways can Jill select 2 different books?

answer is 30 but I got 15.

let n=6

let r=2

n!/r!(n-r)! =15...

I dont get it

PLEASE HELP! my exam is next week and I still don't know how to solve these

Could anyone PLEASE help me to solve these problems??

#37: The numbers (1,2,3,6) have an average (arithmetic mean) of 3 and a variance of 3.5. What is the average (arithmetic mean) and variance of the set of numbers (3,6,9,18)

answer is 9, 31.5

How do you find variance?

Isn't it

S^2= sum (x-average)^2 / n-1 ?

I don't know how to get 31.5!

#38. Jill has 6 different books. in how many ways can Jill select 2 different books?

answer is 30 but I got 15.

let n=6

let r=2

n!/r!(n-r)! =15...

I dont get it

PLEASE HELP! my exam is next week and I still don't know how to solve these