Question

4.
Find S25 for 3 + 7 + 11 + 15 + …
A. 1263
B. 1267
C. 1271
D. 1275
5.
Find S11 for 3 + 1 + (-1) + (-3) +…
A. -77
B. -75
C. -73
D. -71
6.
The following sequence is arithmetic.
2, -2, 2, -2, 2,…
A. true
B. false

Answer 1

The formula for the sum of n terms of an arithmetic sequence is
\[S=\frac{n}{2}[2a+(n-1)d]\]
In question 4 the value of n is 25, a = 3 and d = 4. So just plug these values into the formula.

Answer 2

so 4 would be D ?

Answer 3

Yes, D is the correct choice. Can you do question 5 now?

Answer 4

is it B ?

Answer 5

In question 5, a = 3, d = -2 and n = 11. Can you plug these values into the formula and calculate again?

Answer 6

how do you find D ?

Answer 7

If you mean d in the formula, d is the common difference between terms. It is found by taking the second term and subtracting the first term from it. So in question 5, the second term is 1 and the first term is 3.
d = 1 - 3 = -2

Answer 8

Okay , So would my answer be A?

Answer 9

(11/2) [2(3)+(11-1)-2] This how i typed it in my calculater

Answer 10

Good work! A is the correct choice for question 5.

Answer 11

Okay Thanks and For 6 i chose False !

Answer 12

is that correct ?