Question
There are 90 students in a classroom. How many relationships are there in this classroom? Show how you got this.
Hint: Consider this 2 students in the class would be 1 relationship, whereas 7 students in the class would yield 21 relationships.
What I think: I'm super stuck on this. I think you use factorials but how?
Hint: Consider this 2 students in the class would be 1 relationship, whereas 7 students in the class would yield 21 relationships.
What I think: I'm super stuck on this. I think you use factorials but how?
Answers
Damon
combinations of 2 at a time?
for example for 7 students
n!/[ 2! (7-2)! ]
= 7 /{2*5!}
= 7 * 6 /2 = 21 well that checks so
90! /[ 2!(88!) ]
= 90 * 89/2
= 45*89
= 4005
for example for 7 students
n!/[ 2! (7-2)! ]
= 7 /{2*5!}
= 7 * 6 /2 = 21 well that checks so
90! /[ 2!(88!) ]
= 90 * 89/2
= 45*89
= 4005
Damon
= 7! /{2*5!}
= 7 * 6 /2 = 21 well that checks so
= 7 * 6 /2 = 21 well that checks so