Question

Difficult problem.. lesson; arithmetic series >attachment.

Answer 1

-1650

Answer 2

How did you get that? I got 3600

Answer 3

dont you just add up all the terms?

Answer 4

30, 10, -10, -30, -50, -70 etc...

Answer 5

Im not sure thats how.. i know your supposed to find a1 by doing:
a1 = 50 - 20(1) = 30
then finding the 15th term..
a15= 50 - 20(15) = 450
then using this formula:
sn = n(a1 + a2)/2

Answer 6

50-20(15) isnt 450. its a negative number.

Answer 7

its -250

Answer 8

no because 50 - 20 is 30 then times 15 is 450 right?

Answer 9

I used this example

Answer 10

nooo lol!! thats like the biggest no no in math. ever heard of p.e.m.d.a.s? you multiply first then subtract! so its 50-20(15). you first multiply 20(15) to get 300. then you do 50-300

Answer 11

oh wait sorry thats the wrong one

Answer 12

here it is

Answer 13

I know pemdas. Parthesis, exponets, *, /, - , but here in that example it doesnt do it that way.

Answer 14

oh haha that makes sense now different question

Answer 15

Oh wait yess your right.. they did do it that way. cant believe i ddint see that.

Answer 16

lol sorry

Answer 17

thanks.. i see my mistake now. I will do it again :)

Answer 18

I get -1650 too. thanks for that!