20% of the student body of Tyson Middle School is in the band. If the student population of Tyson Middle School is 680. how many students are in the band? A. 68
B. 136
C. 78
D. 120 ​

there are no short passages to look at

, and

for

step-by-step explanation:

we can analyze the pattern at which the terms increase. let us denote , , , so that we can call

note the following:

the pattern: to get the next term value, we just add the next term number (e.g. 1st, 2nd, to the previous term value (term values are the given numbers in the question, 1, 3, 6, 10, 15,

from , to get to , we add

from , to get to , we add

etc.

we need to form a recursive formula, a formula that has the next term as a function of the previous term. so a possible recursive formula can be

, and for

just took the test and my answers down below!

step-by-step explanation:

check the pic :