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1. (Original post by Acrux)
Un=k+(100-1)k
=100k
Not quite. You've correctly identified that a, the first term, = k, and the difference is k in the series, so Un = k + (n-1)k.

You don't know what n is, but you know that Un, the final term (since there are n terms) is .... so ...
2. (Original post by Math12345)
Careful.

Count the bits in the brackets (1,2.....)
Brackets is from 1- 100 which is 100 terms
3. (Original post by Acrux)
Brackets is from 1- 100 which is 100 terms
No it's from 1 to 100/k.

So how many terms?
4. (Original post by SeanFM)
Not quite. You've correctly identified that a, the first term, = k, and the difference is k in the series, so Un = k + (n-1)k.

You don't know what n is, but you know that Un, the final term (since there are n terms) is .... so ...
so 100=k+(n-1)k
100=kn
n=100/k

so you cant assume there are 100 terms as it goes from k to 100?
5. (Original post by Acrux)
so 100=k+(n-1)k
100=kn
n=100/k

so you cant assume there are 100 terms as it goes from k to 100?
Correct.

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