Maths sequence homework Q: can anyone help??

[JoyceDivision]

DD totally blank on this, can anyone help?

What is the 100th sequence of:

6, 12, 16, 21 (ddput 500)

25,27,29,31 (DD put 200)

2, 0, -2, -4 (DD put -200)

I'm hopeless at maths but DD seems to be guessing rather than knowing how to work it out

I'm not going to tell her if the correct answer is different but I do want to see if she is way out...

6, 12, 16, 21 (ddput 500)
Are you sure last number isn’t 20? If so -Rule is 4n+ 2 so 100th term is 402
25,27,29,31 (DD put 200)
Rule is 2n+23 so 100th term is 223
2, 0, -2, -4 (DD put -200)
Rule is -2n + 4 so 100th term is -196

Thankyou!

Sorry, first line should read 6, 11, 16, 21

Disagree with the first answer -
n(1) gives 6, but n(2) gives 10. n(3) 14 and n(4) 18.

Others look right.

Try 5n +1

Yep. Agreed. So 501.

Sorry yes the first one should be 5n+1. Read too quickly and jumped to 4n!

Haha thank you everyone!

I am going to gently suggest DD looks back over it gaaaaaaah

So is it +1 because we can go back along the sequence to 1?

If the differences are the same then it is an arithmetic sequence, so you have the difference times n (if the difference is 5, then it would be 5n). Then plus or minus the number that would give you the right sequence. 6, 11, 16, 21, difference is 5, so 5n, then you can see you need to add one to get the first terms of the sequence, so it is 5n+1.

She’s not guess ping, she’s just missed the last step.

She’s figured out the equal step sizes which gives her 5n and multiplied by 100.

What she needs to do next is to figure out the difference between what the term would be if the sequence was 5n and what the sequence in the question is.

You can also work out it's +1 at the end by finding the 0th term - the number that would come before the first term in the sequence. Which kids often find easier to do without making an error than other methods.

www.bbc.com/bitesize/guides/z7j2pv4/revision/5

This might make it clearer.