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# Arithmetic series help watch

1. Hi,

Could someone please tell me how to do this question.

A shop assistant is arranging a display of a triangular array of tins so as to have one tin in the top row,two in the second,three in the third and so on. If there are 100 tins altogether,how many rows can be completed and how many tins will be left over?

So far I have a=1 and d=1 and I don't really know what to do from there

Thanks.
2. the first is a the last is a+(n-1)d

the sum = n/2 (a+l)

if the sum is 100 sub in and solve for n
3. (Original post by Goods)
the first is a the last is a+(n-1)d

the sum = n/2 (a+l)

if the sum is 100 sub in and solve for n
So the last term is n?
4. n is the number of rows

solve sum = n/2 (2a + (n-1)d ) (rearrangment of what i said above)

solve the quadratic discard the negative value. You have to round down to the nearest integer (you cant have more cans) to get the number of cans in the bottom row then you can work out the number left over.

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Updated: April 17, 2013
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