Answer:
66
Step-by-step explanation:
If there are <em>n</em> students, then the number of pairs is
.
With 12 students,
pairs can be formed.
The reason the formula works is this: Each of the 12 students can be paired with 11 other students (no student is paired with him/her self). But counting 12 x 11 = 132 counts each pair <u>twice</u>. Example: student A can be paired with student B,..., student B can be paired with student A. The pair was counted two times.
See the attached image that shows pairings of 5 students. There are
5(5 - 1)/2 = 5(4)/2 = 10 pairs.
18+30=48
48+40=88
88+40=128
128+50=178
Thats all i found so far in the pattern
30,40,40,50
then it drops
by 140 then adds by 30..
I dont know how else to explain it
Answer:
First get the formula for your pattern in the form of TN. Where d represents your difference and a represents your first term. Then equate the -401 to your formula and solve for n