Answer:
There were 378 exchanges of Valentine's greetings.
Step-by-step explanation:
If every student exchanged Valentines greeting to each other, then:
Student 1 to 27
Student 2 to 26
Student 3 to 25
Student 4 to 24
and so on.
Total number of Valentine greetings exchanged = [n (n-1)]/2
Where n = 28
Total = [28 (28-1)]/2
= [28 (27)]/2
= (14)(27)
= 378
