What is the sum of the first 19 terms of an arithmetic series with a rate of increase of 7 and a7 = 46?

A. 1,197
B. 1,273
C. 1,373
D. 1,423
E. 1,327

Question

What is the sum of the first 19 terms of an arithmetic series with a rate of increase of 7 and a7 = 46?

A. 1,197
B. 1,273
C. 1,373
D. 1,423
E. 1,327

hartnn · Answer

d= +7 
from a7, and $a_n=a_1+(n-1)d$
you will get a1 
then just apply sum formula....you have it ?

anonymous · Answer

No I do not unfortunately.

hartnn · Answer

sum of 'n' term of arithmetic sequence is 
$\large S_n = (n/2)[2a+(n-1)d]$

anonymous · Answer

Looks like a foreign language to me..

hartnn · Answer

just a formula!
you will have n,a1,d values, just plugging in....

a1 you will get from the formula an = a1 + (n-1)d
n=7, a7=46,d=+7

anonymous · Answer

20?

hartnn · Answer

how ?

anonymous · Answer

I plugged in the numbers wrong I guess.

hartnn · Answer

yeah, 
46 = a1 + 6*(7)
a1 = 46-42 =... ?

anonymous · Answer

4?

hartnn · Answer

yeah, a1 = 4
n=19, d=+7 
plug these in 
$\large S_n = (n/2)[2a_1+(n-1)d]$

anonymous · Answer

I cant figure it out

hartnn · Answer

you can't plug in values ? 

S19 = (19/2) * (2*4 + 18*7) =... ?

anonymous · Answer

I got 1,273 !

hartnn · Answer

i get that too :)

anonymous · Answer

thanks :D

hartnn · Answer

welcome ^_^

anonymous · Answer

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