They are multiplying by two .
Answer:
Step-by-step explanation:
Let a , b , c & d be the no. of chairs in hall A , B , C & D respectively.
Given,
b = 4a
c = a + 15
d = a + 8 + 4a = 5a + 8
Now,
Total no. of chairs (T) = a + b + c + d
= a + 4a + a + 15 + 5a + 8
= 11a + 23
Now,
Average chairs in each hall (Avg) = T/4
= (11a + 23)/4
Answer:
Step-by-step explanation:
8. 







9. 


10. 


11. 6.9 < x - 2.3
+ 2.3 + 2.3
9.2 < x = x > 9.2
Hope this helps!
The question is an illustration of related rates.
The rate of change between you and the ball is 0.01 rad per second
I added an attachment to illustrate the given parameters.
The representations on the attachment are:

---- the rate

First, we calculate the vertical distance (y) using tangent ratio

Substitute 100 for x


Differentiate both sides with respect to time (t)

Substitute values for the rates and 

This gives


Divide both sides by 2


Hence, the rate of change between you and the ball is 0.01 rad per second
Read more about related rates at:
brainly.com/question/16981791