A child wishes to build up a triangular pile of toy bricks so as to have 1 brick in the top row, 2 in the second, 3 in the third and so on. If he has 100 bricks, how many rows can he complete and how many bricks will he have left over?
I worked out the answer is 13, but my method was using the triangle numbers e.g. 1,3,6,10,15......
Whats the more efficient way?
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Geometric Sequence/Arithmetic Series help watch
- Thread Starter
- 03-12-2014 22:23
Study help in partnership with Birmingham City University
- 09-12-2014 23:05
Use the formula for the sum of the first n natural numbers: s = n(n+1)/2
set s as 100, find n and round down our answer to get number of rows
then use the rounded down value to find the actual sum, call this number x
(100 - x) is your final answer