math
posted by Jon on .
Hi I need someone to check my answers I'll show whatever work I have but for time purposes I'll just post my answers because I think I have most of them correct. Thanks!
1)Find the 20th term of the arithmetic sequence in which a1=3 and d=7.
A)143
B)136
C)140
D)133
I chose B
2)Write an equation for the nth term of the arithmetic sequence 3,3,9,15...
A)aN=n+6
B)aN=6n+9
C)aN=6n9
D)aN=n3
I chose B
3)Find the two arithmetic means between 4 and 22.
A)10,16
B)8,16
C)8,12
D)13,13
I chose A
4)Simplify: Find Sn for the arithmetic series in which a1=3,d=1/2,and aN=15
A)225
B)9
C)45
D)210
I chose B
5)ok this one's tricky to type but its with sigma so here it is.
There is a sigma sign and there is an 8 on the top of it and k=3 below. In parentheses to the right is (403k) and the question is Find.
A)45
B)282
C)90
D)141
I chose D. this question is tricky but if you read it slowly and you know about sigma you'll be able to help. Thanks again.

Your #2 and 4 are not correct
#2:
you picked B which is t_{n} = 6n+9
if you let n=1 you get 15 as your first term, you should obtain 3
doesn't C give you that result?
#4:
t_{n} = 15
15 = 3 + (n1)(1/2)
12 = (n1)/2
24 = n1
n=25
So S_{25} = 25/2[6 + 24(1/2)]
= 25/2[18]
= 225 which is A 
ok thanks. Did you check the others?

the others were ok