Answer:
The first 4 guests can arrive in 32,760 ways.
Step-by-step explanation:
The order in which the guests arrive is important. For example, A,B,C,D is a different outcome to B,A,C,D. So we use the permutations formula to solve this question.
Permutations formula:
The number of possible permutations of x elements from a set of n elements is given by the following formula:

In this question:
4 guests from a set of 15. So

The first 4 guests can arrive in 32,760 ways.
Answer:
y = 1/2
Step-by-step explanation:
;)
Answer: The length of JF = 16 units.
Step-by-step explanation:
Given: In triangle DEF, segment DJ is a perpendicular bisector of side EF.
i.e. DJ is perpendicular to EF and DJ divides EF into two equal parts EJ and JF. [The perpendicular bisector is a line that is perpendicular to a line segment and splits it into two congruent segments.]
If EJ is 3y-8 and JF is 7y-40.
Then, 
![\Rightarrow\ 7y-3y=40-8\\\\\Rightarrow\ 4y=32\\\\\Rightarrow\ y=8 \text{ [Divide both sides by 4]}](https://tex.z-dn.net/?f=%5CRightarrow%5C%207y-3y%3D40-8%5C%5C%5C%5C%5CRightarrow%5C%204y%3D32%5C%5C%5C%5C%5CRightarrow%5C%20y%3D8%20%5Ctext%7B%20%5BDivide%20both%20sides%20by%204%5D%7D)
JF= 7(8)-40 =56-40= 16 units
Hence, the length of JF = 16 units.