Question

The sum of the first six terms of an arithmetic sequence is 99. If the 6th term is 39.
a)what is the sum of the 3rd term and 4th term?
b)which is the 3rd term?
c)write the sequence?​

Answer 1

Answer:

First I subtracted 39 from 99 to get 60 which is the sum of the previous 5 terms. Since it was given that this is an Arithmetic Progression, I decided to start subtracting the same value from each successive term starting with 39. I started subtracting 9s because of the two numbers I was given, there were three 9s. (Not scientific, I know, but I had to start somewhere and that tells you why I started with 9.)

39-9=30

30-9=21

21-9=12

12-9=3

3-9=-6

-6+3+12+21+30+39=99

(I got lucky!)

Answer:

12 is the third term

33 is the sum of the third and fourth terms