Posted by **Marissa** on Sunday, August 26, 2007 at 12:00pm.

1)Find the 20th term of the arithmetic sequence in which a1=3 and d=7

a.143

b.136

c.140

d.133

an=a1+(n-1)d

a20=3+(20-1)7

a20=3+(19)7

a20=3+133

answer=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=6n-9

d.an=n-3

an=a1+(n-1)d

an=3+(n-1)-6

an=3-6n+6

answer=b

3)Find the two arithmetic means between 4 and 22

a.10,16

b.8,16

c.8,12

d.13,13

an=a1+(n-1)d

a6=4+(6-1)d

22=4+6d

answer=a

4)Simplify:Find Snfor the arithmetic series in which a1=3,d=1/2,and an=15

a.225

b.9

c.45

d.210

Sn=n/2(a1+an)

Sn=15/2(3+15)

answer=b

5)I don't know how to type this but its like this in my book.

Find; 8 is on top of the sigma notation and k=3 is at the bottom(40-3k) is on the right side

a.45

b.282

c.-90

d.141

40-3(3)=40-9=31

40-3(4)=40-12=28

40-3(5)=40-15=25

40-3(6)=40-18=22

40-3(7)=40-21=19

40-3(8)=40-24=16

answer=d

- algebra -
**bobpursley**, Sunday, August 26, 2007 at 2:37pm
2. Isn't a1=-3, and d=+6 ?

3--I have no idea what the question is asking.

5.

Sum= sigma(k=3,8) of (40-3k)

(40-3*3)+(40-3*4) + ... as you wrote the terms.

It will break down to

40*(8-2) - 3(3+4+5+6+7+8)=240-3*33=240-99= 141 as upi determined.

=

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