find sum of the 1st 20 terms in the arithmetic series 5,8,11,14

Question

amistre64 · Answer

what do we add to get to each next term?

amistre64 · Answer

called a common difference

anonymous · Answer

3

amistre64 · Answer

3 is right :)

so, Sn = n(first+last)/2  if i recall it right

amistre64 · Answer

to determine the 20th term is a20 = 5+3(19) = 62

62+5 = 67*20/2 = 670 ... if my math was good

anonymous · Answer

Oh so it's 670? Thank you so so so much! wow thank you.

amistre64 · Answer

i hope so, id dbl chk with the wolf:

sum (5+3(n-1)) from 1 to 20

amistre64 · Answer

amistre64 · Answer

670 :)

anonymous · Answer

Can you help me with one more? Find the 7th term in the geometric sequence 4,20,11

amistre64 · Answer

20/4 = our common ratio

an = a1 * r^(n-1)

a7 = 4 * (20/5)^6

amistre64 · Answer

your 11 is bad there, is that a typo?

anonymous · Answer

sorry i meant 100

anonymous · Answer

yes :/

amistre64 · Answer

whew!! lol, then yeah; 4*5^6 should do it

anonymous · Answer

so a^7 = 4*5^6?

anonymous · Answer

dd you get 250?

amistre64 · Answer

i think its bigger than that; 5^4 = 25^2 = 625 alone

amistre64 · Answer

625*20 is what id end up with

amistre64 · Answer

12500 perhaps?  hard to do in the head :)

amistre64 · Answer

amistre64 · Answer

i left off the last *5 ....

12500*5=62500