You are Here: Home >< Maths

# C1 Arithmetic sequence help!! Watch

1. Can someone help me answer part c of this question? Question is in attachment!

Attached Images

2. (Original post by mujahid_e3)
Can someone help me answer part c of this question? Question is in attachment!

Use the formula n/2{2A + (n-1)d} = Sum (twice Jill's value)

n = number of terms
A= 1st term
d = common difference

sub in the values you know you get:

20/2{2A + 19 x 30} = 9800
10{2A +570} = 9800
2A +570 = 980
2A = 410
A = 205
3. Use the formula .

In this case, is double your answer to part (b), a is A, n is 20 and d is 30.

Then you can rearrange to find A.
4. (Original post by ttoby)
Use the formula .

In this case, is double your answer to part (b), a is A, n is 20 and d is 30.

Then you can rearrange to find A.
i am finding it hard to rearrange and find a so if you can please show step by step!

Thanks
5. (Original post by fudgesundae)
Use the formula

n = number of terms
A= 1st term
d = common difference

sub in the values you know you get:

20/2{2A + 19 x 30} = 9800
10{2A +570} = 9800
2A +570 = 980
2A = 410
A = 205
^^^^^^^

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: December 3, 2010
Today on TSR

### Cambridge interview invitations

Has yours come through yet?

### Official Oxford interview invite list

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Useful resources

## Make your revision easier

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

Can you help? Study help unanswered threads

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.