Answer:
a) P = 362880 ways
b) P = 2880 ways
Step-by-step explanation:
a) We have four boys and five girls, they are going to sit together in a row of 9 theater seats, without restrictions
We have a permutation of 9 elements
P = 9!
P = 9*8*7*6*5*4*3*2*1
P = 362880 ways
b) Boys must seat together, we have two groups of people
4 boys they can seat in 4! different ways
P₁ = 4!
P₁ = 4*3*2*1
P₁ = 24
And girls can seat in 5! dfferent ways
P₂ = 5!
P₂ = 5*4*3*2*1
P₂ = 120
To get total ways in the above mentioned condition, we have to multiply P₁*P₂
P = 24*120
P = 2880 ways

Refer to the attachment for calculations.
Answer:
- 16
Step-by-step explanation:
Average is calculated as
average = 
Thus for the given 10 numbers we have
= - 5 ( multiply both sides by 10 )
total = - 50
let the number added be x, then
= - 6 ( multiply both sides by 11 )
total + x = - 66, that is
- 50 + x = - 66 ( add 50 to both sides )
x = - 16
The new number is - 16
The answer will be y^2/4 (I’ve written up properly on the photo as I can’t type it)