Question

Series help. *question attached below* will give medal

Answer 1

Can someone help me with part b of this question, please?

Answer 2

nice handwriting :O

Answer 3

Haha, thank you :) @sourwing

Answer 4

Use the formula:
\[\large S _{n}=\frac{n}{2}(2a+(n-1)d)\ ..........(1)\]
Plug in the given values to form a pair of equations in a and d, and then solve.
Do you need more help?

Answer 5

I actually did that using S10 and got lost from there

Answer 6

I need to do the same for S5 too?

Answer 7

Yes, you need a pair of equations, the reason being that there are two unknowns.

Answer 8

Alrighty. Let me work on that

Answer 9

I got -82/11 as my common difference :O Is this correct?

Answer 10

Ohhh nevermind..i did something wrong :O

Answer 11

I've ended up with 82/25 for the common difference :S

Answer 12

My attempt has given a negative value for d, with 0 < d < 1.

Answer 13

-82/25...but this answer just seems odd

Answer 14

But -82/25 is greater than 1. My result for d is negative, with d being less than 1 and greater than 0.

Answer 15

Hmm, let me attempt it again

Answer 16

Still ended up with 82/25

Answer 17

Sorry, my bad :(
d = 82/25 is correct.

Answer 18

:)

Answer 19

And 136/25 for the first term

Answer 20

Yes, a = 5.44. Good work!

Answer 21

Thank you! :)

Answer 22

You're welcome :)